Hebrews chapters 3 and 4 are two short chapters which contain quite a few passages that are often used to teach works Salvation. Chapter 4 is a continuation of a thought that begins in chapter 3, so it makes sense to cover them both in the same article.
After two chapters focused on the person and work of Jesus, the first 6 verses of chapter 3 continue in pretty much the same vein, but instead of contrasting Christ with the angels, like he did in Hebrews 1:4-14, this time the Apostle Paul compares Christ to Moses, pointing out His superiority, which forms part of an argument developed later in the book, where the Testament Christ brought is explained to be better than that of Moses (Hebrews 7:22, 8:6):
Hebrews 3:1-6
1 Wherefore, holy brethren, partakers of the heavenly calling, consider the Apostle and High Priest of our profession, Christ Jesus;
2 Who was faithful to him that appointed him, as also Moses was faithful in all his house.
3 For this man was counted worthy of more glory than Moses, inasmuch as he who hath builded the house hath more honour than the house.
4 For every house is builded by some man; but he that built all things is God.
5 And Moses verily was faithful in all his house, as a servant, for a testimony of those things which were to be spoken after;
6 But Christ as a son over his own house; whose house are we, if we hold fast the confidence and the rejoicing of the hope firm unto the end.
Verse 6 above is the first of the "problem passages" in these chapters. Notice the conditional - only "if we hold fast the confidence an the rejoicing of the hope firm unto the end", will be the house of Christ. Does this refer to becoming a member of the family of God, positionally, based on doing what's prescribed in verse 6?
The answer is a clear no. Not only are those who Paul is addressing called "holy brethren, partakers of the heavenly calling" (Hebrews 3:1) in the passage - which testifies to their positional status in Christ - but the audience is referred to in terms that could only apply to Christians throughout the entire epistle (Hebrews 3:12, 4:3, 4:14-16, 5:12, 6:9-12, 10:19-25, 10:32-36, 12:1-2, etc.), with the Apostle Paul frequently identifying with them, using the words "us", "we", and "our".
We can add to this what we know about the New Birth into God's family being by faith (1 John 5:1, John 1:12, Galatians 3:26), the fact that the New Birth is something spoken of as a present reality, and the fact that it is clarified to be irrevocable (1 Peter 1:23, Ephesians 1:12-14, etc.). Lastly, we can look at the fact that we are already "of the household of God" positionally (Ephesians 2:19: 1 Peter 2:5), and literally serve as the "house" of each member of the Trinity (2 John 1:2: 1 Corinthians 3:16, 6:19, etc.), to dismiss the idea that this is talking about conditionally securing the New Birth based on obeying the latter part of Hebrews 3:6.
So, in what sense will we be "the house of Christ" only if we hold fast in the faith? We will be the children of God, not only positionally, but in practicality and experience, as is spoken of in a similar sense in the following passages:
Philippians 2:14-15
14 Do all things without murmurings and disputings:
15 That ye may be blameless and harmless, the sons of God, without rebuke, in the midst of a crooked and perverse nation, among whom ye shine as lights in the world;
Matthew 5:9
9 Blessed are the peacemakers: for they shall be called the children of God.
Matthew 5:44-45
44 But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you;
45 That ye may be the children of your Father which is in heaven: for he maketh his sun to rise on the evil and on the good, and sendeth rain on the just and on the unjust.
All of the above, like our passage in question, are conditional, and have to do with good works. Notice, not only are we positionally sons, but we are to be "the sons of God, without rebuke" (Philippians 2:15), so that we can be "called the children of God" (Matthew 5:9). Note especially in the last passage, how we already positionally have a "Father which is in heaven" (Matthew 5:45), yet are commanded to be His children. How? In experience.
Continuing in the chapter, the focus shifts from Moses, to the first generation that he led through the wilderness, after the Exodus:
Hebrews 3:7-14
7 Wherefore (as the Holy Ghost saith, To day if ye will hear his voice,
8 Harden not your hearts, as in the provocation, in the day of temptation in the wilderness:
9 When your fathers tempted me, proved me, and saw my works forty years.
10 Wherefore I was grieved with that generation, and said, They do alway err in their heart; and they have not known my ways.
11 So I sware in my wrath, They shall not enter into my rest.)
12 Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living God.
13 But exhort one another daily, while it is called To day; lest any of you be hardened through the deceitfulness of sin.
14 For we are made partakers of Christ, if we hold the beginning of our confidence stedfast unto the end;
Verse 14 above is the second "problem passage" often referred to from this chapter. Notice how similar it is to Hebrews 3:6. Both are "if" conditionals, and both of the conditions are nearly identical. The result for fulfilling the condition is being made a "partaker of Christ". But, isn't every Christian already a partaker of Christ?
In one sense, absolutely. For instance, positionally, we are "in Christ Jesus" (1 Corinthians 1:30), and "we are members of his body, of his flesh, and of his bones" (Ephesians 5:30). There are many such references which state that believers are members of the body of Christ, in the present tense (1 Corinthians 6:15, 12:27, Romans 12:5, etc.).
The kind of "partaking" spoken of in Hebrews 3:14, then, hearkens back to the beginning of the chapter:
Hebrews 3:1
1 Wherefore, holy brethren, partakers of the heavenly calling, consider the Apostle and High Priest of our profession, Christ Jesus;
When we believed in Christ, we began a lifelong journey, just as the children of Israel were led through the wilderness for forty years (Hebrews 3:8-11). Failing, as the children of Israel, to heed the warnings God gives us (Hebrews 3:7-8, 3:13-14), will see that we stray from continuing to partake in the heavenly calling in Christ, to reflect His holiness in this world, in our experience:
Hebrews 12:10
10 For they verily for a few days chastened us after their own pleasure; but he for our profit, that we might be partakers of his holiness.
What consequences does this have? Not only the loss of blessings in this life, and loss of partaking in the inheritance promised to faithful believers (Hebrews 6:11-12, 10:36), but also incurring the partaking of chastisement:
Hebrews 12:6-10
6 For whom the Lord loveth he chasteneth, and scourgeth every son whom he receiveth.
7 If ye endure chastening, God dealeth with you as with sons; for what son is he whom the father chasteneth not?
8 But if ye be without chastisement, whereof all are partakers, then are ye bastards, and not sons.
9 Furthermore we have had fathers of our flesh which corrected us, and we gave them reverence: shall we not much rather be in subjection unto the Father of spirits, and live?
10 For they verily for a few days chastened us after their own pleasure; but he for our profit, that we might be partakers of his holiness.
Above, we see that one of the drivers that God uses to bring wayward children back onto the path of the heavenly calling, is chastisement. Not only does this passage show that it's possible for a "genuine" child of God to go wayward long before "the end" that both of our passages in question so far have mentioned (Hebrews 3:6, 3:14), it also shows that God, rather than send such a one to Hell, loves them instead, and only chastens them with that in mind.
Finally, we can discuss a line of thought that spans most of chapters 3 and 4, and that is God's rest. This section is a bit hard to cover, because of its length - almost the entirety of Hebrews 3:7-4:11 deals with this subject.
To begin, it's helpful to read an uninterrupted reprint of the relevant passage:
Hebrews 3:7-4:11
7 Wherefore (as the Holy Ghost saith, To day if ye will hear his voice,
8 Harden not your hearts, as in the provocation, in the day of temptation in the wilderness:
9 When your fathers tempted me, proved me, and saw my works forty years.
10 Wherefore I was grieved with that generation, and said, They do alway err in their heart; and they have not known my ways.
11 So I sware in my wrath, They shall not enter into my rest.) (Psalm 95:7-11)
12 Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living God.
13 But exhort one another daily, while it is called To day; lest any of you be hardened through the deceitfulness of sin.
14 For we are made partakers of Christ, if we hold the beginning of our confidence stedfast unto the end; 15 While it is said, To day if ye will hear his voice, harden not your hearts, as in the provocation.
16 For some, when they had heard, did provoke: howbeit not all that came out of Egypt by Moses.
17 But with whom was he grieved forty years? was it not with them that had sinned, whose carcases fell in the wilderness?
18 And to whom sware he that they should not enter into his rest, but to them that believed not?
19 So we see that they could not enter in because of unbelief.
1 Let us therefore fear, lest, a promise being left us of entering into his rest, any of you should seem to come short of it.
2 For unto us was the gospel preached, as well as unto them: but the word preached did not profit them, not being mixed with faith in them that heard it.
3 For we which have believed do enter into rest, as he said, As I have sworn in my wrath, they shall not enter into my rest: although the works were finished from the foundation of the world. (Psalm 95:11)
4 For he spake in a certain place of the seventh day on this wise, And God did rest the seventh day from all his works. (Genesis 2:2)
5 And in this place again, they shall not enter into my rest.
6 Seeing therefore it remaineth that some must enter therein, and they to whom it was first preached entered not in because of unbelief:
7 Again, he limiteth a certain day, saying in David, To day, after so long a time; as it is said, To day if ye will hear his voice, harden not your hearts.
8 For if Jesus had given them rest, then would he not afterward have spoken of another day.
9 There remaineth therefore a rest to the people of God.
10 For he that is entered into his rest, he also hath ceased from his own works, as God did from his.
11 Let us labour therefore to enter into that rest, lest any man fall after the same example of unbelief.
From the above, notice:
Specifically, the last portion of this passage warrants highlighting:
Hebrews 4:6-11
6 Seeing therefore it remaineth that some must enter therein, and they to whom it was first preached entered not in because of unbelief:
7 Again, he limiteth a certain day, saying in David, To day, after so long a time; as it is said, To day if ye will hear his voice, harden not your hearts.
8 For if Jesus had given them rest, then would he not afterward have spoken of another day.
9 There remaineth therefore a rest to the people of God.
10 For he that is entered into his rest, he also hath ceased from his own works, as God did from his.
11 Let us labour therefore to enter into that rest, lest any man fall after the same example of unbelief.
The point of verses 6 through 9 is to emphasize that if this "rest" were something that was no longer on offer, then it wouldn't have been preached to David, long, long after the Exodus. "There remaineth therefore a rest to the people of God" (Hebrews 4:9) - this looks to the future.
Then, verse 10 emphasizes that once that rest is obtained, the time for work is over - therefore, verse 11 says - "let us labor to enter into that rest", now, while there is still time and the opportunity to work (Hebrews 3:13, John 9:4).
So, what do we know about the "rest"? It's something to be obtained in the future. It's something that requires perseverance in faith and good works, even for "the people of God". And, clearly from the context of these warnings, it's something not guaranteed to all believers (Hebrews 3:12-13, 4:11).
All of this leads us to the conclusion that this "rest" is an inheritance of something in the New Earth, a better rest than the one that we simply are guaranteed by faith (Matthew 11:28-30).
We can look at the primary example used in the passage - the first generation of the children of Israel, who almost all perished in the wilderness. Did all of them go to Hell, because they didn't persevere in faith? Of course not. They simply failed to inherit the promised land. While our entrance into Heaven is by faith (John 3:5: 1 John 1:5), increasing our inheritance - obtaining a greater rest, or a more "abundant entrance" (2 Peter 1:10-11) - is predicated on persisting in faith and works:
Colossians 3:24
24 Knowing that of the Lord ye shall receive the reward of the inheritance: for ye serve the Lord Christ.
Hebrews 6:12
12 That ye be not slothful, but followers of them who through faith and patience inherit the promises.
Hebrews 10:36
36 For ye have need of patience, that, after ye have done the will of God, ye might receive the promise.
Once all of the rewards and inheritance passages, like the above, and the passage in question, are relegated to a binary Heaven or Hell outcome, our scale is lost. Instead of getting a gradually better inheritance corresponding to our performance, we now have a win-or-lose scenario. This is a problem, since none of us are perfect, and so most of professing Christianity adopts the agnostic position of being completely clueless as to just how good one has to be to make the final cut.
However, once the Biblical doctrine of rewards and inheritance in distinction from Salvation is recovered, we can now more easily see that there is a spectrum, or a gradient, on which all believers fit, according to their works (Matthew 16:27, Revelation 22:12). Passages like Hebrews 3 and 4, then, fit well within the scope of what is describing one of these rewards, given for faithful service.
For further reading on the topic, I'd point to the article The Bible's Teaching on Eternal Rewards.
This section from the book of Hebrews may be perplexing to a new believer. However, once it's understood that what stands to be gained or lost is not Salvation, but blessings in this life, and rewards in the world to come, the chapters fall into place, and their original motivational voice is restored (Hebrews 13:22).
Neither this passage, nor the book of Hebrews, is evangelistic in intent. This is an epistle written to Jewish believers, who are facing the difficulty of being rejected by their brethren after the flesh. These chapters are part of an attempt to galvanize them into not abandoning their profession, and lapsing back into temple Judaism, but rather to spur them on to faithfully persevere, and so inherit all that God has for them.