What promise does God make concerning the work He begins in believers?

The promise made by God regarding the work He begins within believers is found in Philippians 1:6, which emphasizes that He who began a good work in you will perform it until the day of Jesus Christ. This truth offers deep comfort and assurance, affirming that salvation is not just a one-time event but a lifelong process in which God actively participates. Unlike human efforts that may falter, God's work is perfect and ongoing, ensuring that those whom He calls will be preserved and brought to completion.