Let the peace of Christ rule in your hearts, to which indeed you were called in one body; and be thankful. (Col 3:15)

Peace

• Peace I leave with you; My peace I give to you; not as the world gives do I give to you. Do not let your heart be troubled, nor let it be fearful. Jn 14:27
• εἰρήνη eirḗnē tranquility ⇔ peace n. — the absence of mental stress or anxiety, mainly that results from a proper recognition of salvation’s worth. 
• Peace = a state of tranquillity or quiet, harmony in personal relationships. ^[1]
• Peace of Jesus is bigger and better than any peace we could ever imagine or experience.
• Peace does not mean that we should be quiet in our actions, but to acknowledge it by sharing peace with others and invite others to Christ.
• The war-torn gates of hell can’t stand up to the commanding peace Jesus brings.^[2]
• Peace within you => Inner peace 
• If the peace of Christ rules the heart, then every decision made and every action taken will have the quality of peace ^[3]

Rule

• It means “to preside at the games and distribute the prizes.” In the Greek games, there were judges (we would call them umpires) who rejected the contestants who were not qualified, and who disqualified those who broke the rules. When we obey the will of God, we have His peace within; but when we step out of His will (even unintentionally), we lose His peace. ^[4]

Heart

• The heart is the center and depth of personal experience.
• Definition => Heart (internal feature) — the locus of a person’s thoughts (mind), volition, emotions, and knowledge of right from wrong (conscience) understood as the heart.
• Character is the reflection of the ingredient of the heart.
• Peace within you and with Christ will produce good character.
• Paul is not saying that the peace is in our hearts; he says that the peace should rule “in the heart.” ^[5]

Body

• The heart is inside the body.
• The church, as the body of Christ, must acknowledge the peace of Christ. 
• If there is no peace inside, then there should not be any sort of unity as corporately.

Thankful

• Be thankful to God and praise Him because of His peace in us.
• When there is peace in the heart, there will be praise on the lips: “And be ye thankful” (Col. 3:15). The Christian out of God’s will is never found giving sincere praise to God. When David covered up his sins, he lost his peace and his praise (Pss. 32; 51). When he confessed his sins, then his song returned. ^[6]

For Further study

Jn 14:27; Ro 12:5; 14:19; 1 Co 7:15; 10:17; Eph 2:16; 4:4; Php 4:7; Col 3:17; 1 Th 5:18