God Finishes What He Starts
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: (Philippians 1:6)
No doubt we have all used this verse to argue for assurance of salvation. And to be sure, we find in the verse an excellently concise statement of eternal security. We have confidence, which is a sign of faith. We have Christ, which is salvation. We have an important promise - "he which hath begun a good work in you will perform it until the day of Jesus Christ." All the elements from which we can be assured that Christ does not lose a Christian.
But eternal security is not Paul's point in this verse. The book of Philippians is an extended "thank you note." Paul is writing to thank the Philippians for a gift they recently sent.
I thank my God upon every remembrance of you... For your fellowship in the gospel from the first day until now. (Philippians 1:3, 5)
Notwithstanding ye have well done, that ye did communicate with my affliction. Now ye Philippians know also, that in the beginning of the gospel, when I departed from Macedonia, no church communicated with me as concerning giving and receiving, but ye only. For even in Thessalonica ye sent once and again unto my necessity. (Philippians 4:14-16)
In Philippians 1:6, Paul is in the middle of telling these believers how he thanks God for them. He says, "Always in every prayer of mine for you all making request with joy, For your fellowship in the gospel from the first day until now; Being confident of this very thing..."
And he goes on to express his confidence, that "he which hath begun a good work in you..." --- that is, the good work of generosity in supporting him and contributing to his "necessity" --- "...will perform it until the day of Jesus Christ."
So then, Paul is not speaking of salvation in this verse. He is speaking of their generous hearts, of their fellowship with him in the gospel. Paul attributes this good work, not to their natural disposition or propensity to be charitable, but to the Lord, Who began this good work in them.
Paul is confident that their generosity and fellowship with him in the gospel will continue, because the same Lord Who began this good work in them will perform it until the day of Jesus Christ. He had confidence that this would not be a passing or a fading virtue. They would not turn back from it or faint in the day of adversity. Well begun is half done, but they would continue in that good work. And he had this confidence, not because he knew their character, but because he knew Who propelled them to do this.
"For it is God which worketh in you both to will and to do of his good pleasure."(Philippians 2:13)
By implication, we can and rightly do apply this to eternal security. If their spirit of generosity would not fail because it was God working in them, then surely their salvation would not fail either. Christ began that good work in them, the good work of generosity, because Christ had begun a more important work in them - the work of salvation. Christ would perform the one because He will perform the other.
And thus, Philippians 1:6 strengthens our conviction that the believer's security is both sure and eternal.