The doctrine of the final perseverance of the saints has as its corollary the salutary teaching that the saints are the people who persevere to the end.
F.F. Bruce
There is no question in the Scripture about the eternal security of those truly regenerated by the Holy Spirit. One should be careful at this point to note that this is no “once saved always saved no matter what you do” doctrine. Indeed, “faith without works” is not the sign of spiritual sickness (or backsliding), but death (Jas. 2:17). The biblical doctrine, therefore, is once saved always saved and that you will keep on doing what God says because you are dead to sin and alive to Christ (Rom. 6:2). All pretenders will receive judgment (Matt. 7:21–23). All regenerates will persevere.
Leonard Coppes
That doctrine of the final perseverance of the saints is, I believe, as thoroughly bound up with the standing or falling of the gospel as is the article of justification by faith. Give that up, and I see no gospel left.
C.H. Spurgeon