Because we are chosen by God, we are holy and beloved (Col 3:12). Because we are holy and beloved, we can cover ourselves with mercy, kindness, humility, meekness, long-suffering, and forgiveness (Col 3:12-13). Then, by God's grace, we can cover this covering of virtue with the covering of love (Col 3:14). "Above all, let your love for one another be constant, for love covers a multitude of sins" and a multitude of virtues (1 Pt 4:8). Covered in virtue and love, obviously "peace must reign in your hearts" (Col 3:15).
Under these circumstances, we dedicate ourselves to thankfulness (Col 3:15). Therefore, "sing gratefully to God from your hearts in psalms, hymns, and inspired songs. Whatever you do, whether in speech or in action, do it in the name of the Lord Jesus. Give thanks to God the Father through Him" (Col 3:16-17).
We have reason to be thankful. Christ's peace is the reason. We have reasons to be peaceful. Virtue and love are the reasons. We are capable of being virtuous and loving because we are holy and beloved. We are holy and beloved because God has chosen us.
Thank You, Lord, for Your love and grace.