15 Let the peace of Christ rule in your hearts, since as members of one body you were called to peace. And be thankful. 16 Let the message of Christ dwell among you richly as you teach and admonish one another with all wisdom through psalms, hymns, and songs from the Spirit, singing to God with gratitude in your hearts. 17 And whatever you do, whether in word or deed, do it all in the name of the Lord Jesus, giving thanks to God the Father through Him.
One commentary on verse 15 above begins by saying
All these virtues, however, along with the love which binds them together, must have their deep living foundation in the peace of Christ, which reigns in the heart, and their abiding incitement in gratitude towards God for the salvation received in Christ Meyer’s NT Commentary
Of course the virtues he is talking about are in the preceding verses
12 Therefore, as God’s chosen people, holy and dearly loved, clothe yourselves with compassion, kindness, humility, gentleness and patience. 13 Bear with each other and forgive one another if any of you has a grievance against someone. Forgive as the Lord forgave you. 14 And over all these virtues put on love, which binds them all together in perfect unity.
Of course the key virtue is love which comes from the heart! Do you find it interesting Paul does not say Let Christ rule in your hearts, but instead says Let the peace of Christ rule in your hearts? Maybe a few other verses can give us some insight to that.
Peace I leave with you; my peace I give you. I do not give to you as the world gives. Do not let your hearts be troubled and do not be afraid.
And the peace of God, which transcends all understanding, will guard your hearts and your minds in Christ Jesus.
If you are troubled by the phrase rule in your heart, consider the meaning is intended as a director or arbiter so that the peace which God gives to the souls presides over the heart while preserving everything in its place, saving it from tumult and disorder for the soul all too often is given over to influences leading to all sorts of passions and excitements (extracted and paraphrased from Barnes’ Notes on the Bible).
If we are thankful (v15) and have gratitude in our hearts (v16), then if our actions whether in word or deed, [are] do[ne] all in the name of the Lord Jesus, giving thanks to God the Father through Him we will have a peace in our hearts beyond our own understanding for For He Himself is our peace (Ephesians 2:14a).
Have a Great Day and may His peace rule in your heart.