Perseverance Depends On
Perseverance does not depend on man, but rather depends upon (1) God's Decree of sovereign election, (2) God's everlasting love for the elect, (3) Christ's perfect work, (4) God's Oath and Promise, (5) the Holy Spirit in the believer, (6) the Seed of God in the believer and (7) the perfect New Covenant wherein they find themselves.
The Decree Of Election
The fact is: God chooses who gets saved, and leaves the rest in their sins to be damned. God, by His almighty power, has called them effectually through the Gospel and regenerated them, without hindrance from their will, in fact, renewing their wills, giving them faith and repentance so that they may respond positively to the Gospel. God does not go back on His word, nor thinks that He has made a bad choice and wants to change His intentions. If God has chosen who will be saved, He will likewise make sure that they're saved and remain in the state of grace until the end. See our comments on Romans 8:28ff above.
The Unconditional Love Of God
This is very closely connected to elect. God elected us in love. It is His love which moved Him to elect us. He did not elect us to love us, but rather He elected us because He loved us. See Ephesians 1:3-6 and perhaps our comments on Romans 8:28ff above.
The Merit & Intercession Of Christ
It is through the intercession and work of Christ that the redeemed are preserved. It is thanks to His perfect work and continued intercession that their faith may not fail. See our comments on John's Gospel, Romans 8:28ff above and the book of Hebrews which stresses this point a lot.
The Oath Of God
God has promised to preserve the elect. He will not go back on His word. He has called us to salvation and He will preserve us in it. See our brief comment on Hebrews 6:17-20 above.
The Abiding Of Spirit
God has given us His Holy Spirit as a guarantee, as a pledge of all the promises that He has given us and which He will fulfill in the world to come. The Spirit also functions as the seal of God upon the believer. In Ephesians 1 we read:
Eph. 1:13-14 In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit, 14 who is the guarantee of our inheritance until we acquire possession of it, to the praise of his glory.
At the moment we place our faith in Christ we are sealed by the Spirit. What does that mean? John Calvin says the following on this passage:
In whom also, after that ye believed. Having maintained that the gospel is certain, he now comes to the proof. And what higher surety can be found than the Holy Spirit? “Having denominated the gospel the word of truth, I will not prove it by the authority of men; for you have the testimony of the Spirit of God himself, who seals the truth of it in your hearts.” This elegant comparison is taken from Seals, which among men...