The New Testament is clear about the duty of church members in watching out for one another and helping one another persevere (see esp. Heb 3:12-14; 4:1-2, 11; 12:15-16; James 5:19-20). Too often Christians have not learned to think this way. I also often find myself trying to help people see that evangelistic labors, properly understood, include both calling people to initial faith and helping one another persevere in that faith. The following quote from 2 Clement, a 2d century Christian document, illustrates these points well and shows how they were understood early in the history of the church.
Let us therefore repent with our whole heart, lest any of us perish by the way. For if we have received commands, that we should make this our business, to tear men away from idols and to instruct them, how much more is it wrong that a soul which knows God already should perish! Therefore let us assist one another, that we may also lead the weak upward as touching that which is good, to the end that we all may be saved: and let us convert and admonish one another. And let us not think to give heed and believe now only, while we have departed home, let us remember the commandments of the Lord, and not suffer ourselves to be dragged off the other way by our worldly lusts; but coming hither more frequently, let us strive to go forward in the commandments of the Lord, that we all having the same mind may be gathered together unto life. (2Clem 17:1-3, Lightfoot trans.)
Note that earnest evangelism is assumed- “tear men away from idols.” Added to this, the author pleads that his hearers not to sit idly by while professing believers wander from the truth (cf. James 5:19-20).. The remedy for wandering away is “assisting one another”, “admonishing one another”, and gathering frequently with the church (cf. Heb 10:24-25). God has given us the church, one another, fellow believers, to help us persevere.