John Chrysostom

"And be ye thankful." For this is to be thankful, and very effectively, to deal with his fellow-servants as God doth with himself, to submit himself to the Master, to obey; to express his gratitude for all things, even though one insult him, or beat him. For in truth he that confesses thanks due to God for what he suffers, will not revenge himself on him that has done him wrong, since he at least that takes revenge, acknowledges no gratitude. …

Homily on Colossians 8 ↗

Theophylact of Ohrid

Often we are offended by someone, and then two thoughts struggle within us, one of which urges revenge, while the other urges long-suffering. If the peace of God stands within you as the distributor of rewards, that is, as judge and recompenser, then it gives the reward to the thought which commands endurance, and silences the other. Therefore, let the peace of God be the distributor of rewards in you, and not anger, nor contentiousness, nor human peace: for human peace comes from vengeance and retaliation. …

Commentary on Colossians ↗

Thomas Aquinas

Then (v. 15), he urges them to acts of love. He mentions two of these acts, peace and thankfulness, and implies a third, joy. He says, let the peace of Christ rejoice in your hearts. An immediate effect of the love of charity is peace, which is, as Augustine comments, that composure or calmness of order produced in a person by God. Love does this, because when one loves another he harmonizes his will with the other: "Great peace have those who love thy law" (Ps 119:165). …

Commentary on Colossians ↗