“Peace with God” is one thing; “the peace of God” is another. To enjoy the latter, we must first experience the former, for the peace of God, ruling in our hearts, is the result of “peace with God, through our Lord Jesus Christ.”
St. Paul declared by divine inspiration that “[Christ] was delivered for our offences and was raised again for our justification” and that “therefore, being justified by faith,” we, who once were at enmity with God, may enjoy “peace with God through our Lord Jesus Christ” (Rom. 4:25; 5:1). The result of “peace with God” is “the peace of God,” the peace that He gives to His own amid all the troubles of life. This is why the Apostle wrote to the Roman Christians:
“Now the God of hope fill you with all joy and peace in believing” (Rom. 15:13).
While only those who are at peace with God can — and should know “the peace of God,” it does not follow, however, that all those who are at peace with God necessarily enjoy “the peace of God.” Believers can enjoy “the peace of God” only as they practice Phil. 4:6:
“BE CAREFUL [ANXIOUS] FOR NOTHING; BUT IN EVERYTHING, BY PRAYER AND SUPPLICATION, WITH THANKSGIVING, LET YOUR REQUESTS BE MADE KNOWN UNTO GOD.”
As we follow these instructions the promise which follows will certainly be fulfilled.
“THE PEACE OF GOD, WHICH PASSETH ALL UNDERSTANDING, SHALL KEEP YOUR HEARTS AND MINDS THROUGH CHRIST JESUS” (Phil. 4:7).
As believers in Christ “we know that all things work together for good to them that love God, to them who are the called according to His purpose” (Rom. 8:28). Therefore we should not be constantly overwhelmed and defeated by the adversities of life, but should heed the exhortation; “Let the peace of God rule in your hearts” (Col. 3:15). source