Let the peace of God rule in your hearts – May the peace of God “judge, decide, and govern” in your hearts, as the judge did in the Olympic contests of Paul’s day. No heart is right with God where the peace of Christ does not rule, and the continual prevalence of the peace of Christ is the decisive proof that the heart is right with God.

In one body – You cannot have peace with God, in yourselves or among each other, unless you continue in unity; and, as one body, continue in connection and dependence on him who is your only head; to this ye are called.

And be ye thankful – It is a glorious state of salvation, and you should be forever thankful that you are thus privileged.

(From the Commentary of Adam Clarke on Colossians 3:15)