He will complete it!
Complete what? The good work He has started in your life!. When God starts something, He completes it - He is the Alpha (Beginning) and Omega (Ending).
I rejoice with you because what He has started in you is good. Our Lord Jesus clarified 'good work' in John 6:29 as believing in Him. This is the true eternal life you have been called to, in Christ Jesus.
Hold on to Him till the end, because only those who endure to the end shall be saved (Matthew 24:13).
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 - Phillipians 1:6