For I am confident of this very thing, that He who began a good work in you will perfect it until the day of Christ Jesus. (Philippians 1:6, NASB)
Let this promise of God encourage you today. We know we ought to be growing in Christ, but it so often seems we are failing. Sometimes you can look back and see the clear progress you've made in your sanctification. Other times, you look to see how far you have fallen. But the guarantee of the finished work is in Christ, not you. Therein lies the beauty of the promise. And He brings us all the way through.
He who began... It was Christ who began the work within you. He called your name, placed faith within you, and filled you with His Spirit.
Will perfect it… Jesus always finishes what He begins. The end of the matter is in Christ's hands. You will be perfected. He will guarantee it.
Until the day… The work is an ongoing process. In other words, He is at work perfecting you now. Even on the days that you feel you've fallen further instead of progressing closer to Him. He is even using those experiences to bring you to perfection.
Christ is at work in your life bringing you to perfection. He will present you pure on the final day. He began it. He is at work in it. He will complete it. As you strive for holiness, do so knowing it is in His strength. And when you're tired from the striving, rest in knowing that Christ can pick up the slack.