Acts 14:22
22 Confirming the souls of the disciples, and exhorting them to continue in the faith, and that we must through much tribulation enter into the kingdom of God.
This verse is sometimes used to say, in effect, that Christians must "continue in the faith", even "through much tribulation", in order to "enter into the kingdom of God".
In this view:
Is that a valid interpretation?
This verse is, simply put, an exhortation to "continue in the faith", despite the fact that we will encounter "much tribulation". The mention of entering "into the kingdom of God" simply looks towards one's earthly death, whereupon they will be united in their new nature, which is already in Heaven (Ephesians 1:3, 2:6). It's an inevitability, and a statement of fact, not something that hangs in the balance.
To paraphrase - "continue in the faith, because until we get to Heaven, we will have much tribulation". This is a command to steel oneself, and keep a proper mindset. It's like saying, "Until the weekend, we will have a lot of work we have to do". Why say that? So that the person isn't already "in the weekend" in their mentality, but is instead braced for the tough work ahead. The weekend, however, is coming regardless.
This is in keeping with the constant warnings that Christians are given in the New Testament of "tribulation" that they will suffer at the hands of the world (John 16:33: 2 Corinthians 7:4, etc.), so that they will "not be offended" (John 16:1), which is to say, surprised, or caught off guard.
The Word of God is also clear in stating that even if a Christian fails to "continue in the faith", their eternal destiny is secure, because their surety, Jesus, is faithful regardless:
2 Timothy 2:13
13 If we believe not, yet he abideth faithful: he cannot deny himself.
And finally, it should go without stating, that if a Christian had to endure tribulation in order to get to Heaven, others could literally force you to lose your Salvation through torture, and we would be saved entirely by our obedience to Jesus Christ, rendering verses like Ephesians 2:8-9 completely meaningless in any practical circumstance.
This verse does not teach works Salvation, or that perseverance in the faith is a requirement for Salvation. In fact, it actually proves that perseverance in the faith is not a guarantee, otherwise this exhortation would be meaningless.
Instead, this verse is actually a prooftext for Eternal Security, as the fact that every believer will "enter into the kingdom of God", whether they persevere or not, is spoken of as a given. It is an exhortation to expect and endure tribulation, during our short time here on earth, before we get there.