The book of Hebrews contains what is probably the most-quoted exhortation to church membership:
Let us hold fast the confession of our hope without wavering, for he who promised is faithful. And let us consider how to stir up one another to love and good works, not neglecting to meet together, as is the habit of some, but encouraging one another, and all the more as you see the Day drawing near. (Hebrews 10:23-25)
Familiar verses, no doubt. But did you ever notice the reason for this exhortation? The verses that follow explain why it is so vital to meet together and encourage each other. Why is being part of a church such an urgent need?
Let us hold fast the confession of our hope without wavering, for he who promised is faithful. And let us consider how to stir up one another to love and good works, not neglecting to meet together, as is the habit of some, but encouraging one another, and all the more as you see the Day drawing near.
For if we go on sinning deliberately after receiving the knowledge of the truth, there no longer remains a sacrifice for sins, but a fearful expectation of judgment, and a fury of fire that will consume the adversaries. Anyone who has set aside the law of Moses dies without mercy on the evidence of two or three witnesses. How much worse punishment, do you think, will be deserved by the one who has trampled underfoot the Son of God, and has profaned the blood of the covenant by which he was sanctified, and has outraged the Spirit of grace? For we know him who said, “Vengeance is mine; I will repay.” And again, “The Lord will judge his people.” It is a fearful thing to fall into the hands of the living God. (Hebrews 10:23-31)
Meet together, because apostasy is horrible. Encourage one another, because the judgment brought on by apostasy is too terrifying for words.
This is not the only place in Hebrews where this pattern is seen. The same thing is clearly taught in 3:12-19, and 12:15-17 strongly suggests it as well. We are to watch out for each other, exhort each other, do everything possible to keep each other out of sin and strong in the faith, because God will judge the unrepentant apostate with the eternal fires of hell.
If you separate yourself from Christ's people, ultimate apostasy will not be far behind.
If you claim to be Christ's, yet are not part of a church, you are a liar and a fool playing a fool's game. Get in a church - a real church - now. Before it's too late, and you find that, like Esau, you have become so hardened you are incapable of repentance.
49 minutes ago