In Phil. 1:6 we have one of the most definitive Scriptures in the Bible on the doctrine of eternal security, or what I like to call, perseverance of the saints or preservation of the saints.
"Being confident of this very thing, that He which hath begun a good work in you will perform it until the day of Jesus Christ."
Eternal life is a present possession, not something we hope to gain at the end of our life. I believe eternal security and sovereign grace are closely related. If it were not for sovereign grace our salvation would not be eternal.
There are several passages in the Scriptures that are dear to me in regards to eternal sacurity. Here are a few [John 5:24; 10:27-28; Rom. 8:1,29-30; 11:29; 1 Tim. 1:12; Heb. 7:25; 12:1-4; 1 Peter 1:5; Jude 24].
Let me make a few observations from this passage in Phil. 1:6:
1. What is the "good work?" Some would have us believe that it is a project or material work as the prosperity gospel preachers proclaim [Oral Roberts], while others believe Paul is talking about the monetary gift the Philippians' gave Paul. Neither of these fit the verse.
2. Paul is talking about the work of salvation that God began in us and will complete it till Jesus comes again and we are glorified. Regeneration, sanctification and glorification are the three tenses of salvation. Note the reference to their fellowship in the Gospel [v. 5], and confirmation of the gospel [v. 7]. Note that it is a work "in" you.
3. Salvation is God's work from start to finish. He began it and will perform it [perfect, fully accomplish it].
4. God is still doing a work in you. We have not reached the "day of Christ" yet. We are in the process of becoming like Christ [sanctification]. As the song says, "He is still working on me."
5. God will complete the work He began. No true Christian will fall away or quit believing. He began it, He gave us the faith to believe [Eph. 2:89] and He will fully accomplish His purpose in His work of salvation. I like Rom. 8:29-30, it is full of "He" and absent of "me." He begins with those He foreknew to the past tense "has glorified." Some call this the unbreakable chain of redemption. All those foreknew will be glorified.
Thank God for so great a salvation! Even so, come, Lord Jesus!