1 Corinthians 15:1-2

1 Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand;
2 By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain.

Verse 2 above is often confused in two distinct ways:

• The mention of "if ye keep in memory" is used to teach that if someone ever stops believing, they aren't saved
• The mention of "unless ye have believed in vain" is used to teach that there is a type of faith, that though accurate in content, is "spurious", and does not save

Let's examine both of these claims and determine whether they are accurate.

If You Keep in Memory

In the verse in question, in order to be saved one must "keep (the Gospel) in memory". In other words, the ongoing "salvation" being spoken of is contingent upon continuously keeping the Gospel on one's mind.

However, since we know that a believer is saved from Hell even if they stop believing (2 Timothy 2:13), believe a false Gospel later, or join another religion ("heresy", "idolatry" - Galatians 5:19-21), that means that this passage is referring to temporal salvation from the flesh, and other things that would accompany not abiding in the Word.

Common sense also bears witness to this, as a believer who develops Alzheimer's, or endures a traumatic brain injury, may very well forget the Gospel, and even the most faithful among us fail to dwell on it at all times.

What we are seeing, then, is an exhortation to believers to keep the Word of God, and the Gospel in particular, in the forefront of one's mind, as is encouraged in a similar way in the following examples:

John 8:31-32

31 Then said Jesus to those Jews which believed on him, If ye continue in my word, then are ye my disciples indeed;
32 And ye shall know the truth, and the truth shall make you free.

Luke 8:15

15 But that on the good ground are they, which in an honest and good heart, having heard the word, keep it, and bring forth fruit with patience.

James 1:21

21 Wherefore lay apart all filthiness and superfluity of naughtiness, and receive with meekness the engrafted word, which is able to save your souls.

1 Thessalonians 5:21

21 Prove all things; hold fast that which is good.

Hebrews 10:23

23 Let us hold fast the profession of our faith without wavering; (for he is faithful that promised;)

What we see above is ongoing and directed at saved people - "receive", "hold fast", "keep", "continue in" - the Word of God.

What we believe from the Word of God, and the Gospel in particular, does not just fall out of usefulness after we believe it one time. It has an ongoing, sanctifying purpose, and that is what is in mind in the passage in question.

Believed in Vain

The second attack on the Free Grace position from 1 Corinthians 15:2 is the claim that there exists a "spurious" or "vain" faith, which will be identified as "faith without works" (James 2:17, etc.). Therefore, unless one has works, they have "believed in vain", and are consequently not "saved".

This can be refuted by reading further into the chapter, where we see that the Apostle Paul is addressing a false teaching that denied the resurrection, and is pointing out that if Jesus didn't rise from the dead, then their faith is "vain":

1 Corinthians 15:12-17

12 Now if Christ be preached that he rose from the dead, how say some among you that there is no resurrection of the dead?
13 But if there be no resurrection of the dead, then is Christ not risen:
14 And if Christ be not risen, then is our preaching vain, and your faith is also vain.
15 Yea, and we are found false witnesses of God; because we have testified of God that he raised up Christ: whom he raised not up, if so be that the dead rise not.
16 For if the dead rise not, then is not Christ raised:
17 And if Christ be not raised, your faith is vain; ye are yet in your sins.

Twice above, we see what could make one's faith "vain" - the object of their faith. If Christ didn't rise from the dead, they have "believed in vain", that is, they have believed in something useless, because it wasn't true.

So, a simple reading of context dismisses any strange ideas about a "spurious faith", or some other kind of faith, that does not save. Rather, "believing in vain" refers to the object of the faith, and the content of what they believe not being true.

Conclusion

This passage does not present a problem for the Biblical truth that once someone puts their faith in Jesus Christ, they are saved, and given Eternal Life (John 6:47), regardless of what happens later on.

Rather, it's an exhortation to receive "the washing of water by the word" (Ephesians 5:26) by keeping it in memory, and is also a rebuke to those who would deny the resurrection.