There is good reason for this call.
For the apostle had described how that Christ had emptied Himself of His glory (ch. 5:5-11) and had become a man; and how that as Man He is enthroned on high by God the Father. He had further spoken of the Lord upon that throne as our prize (ch. 3:13, 14), and shown that He will make us glorious like Himself (v. 21). With Christ thus before the heart, the call to Rejoice in the Lord can be obeyed.
How often did King David sing, in his days of trial of the God in whom he hoped. We have made Him our hope for time and for eternity, and He is pleased to speak of Himself as the God of hope—the unfailing God, who will never put to shame anyone who places confidence in Him. The more instances we recall of His goodness, and the more eagerly we anticipate the fulfilment of His promises, the greater is our joy and our peace.
We have good cause for joy and for peace, and here is a great verse for us respecting power. Power outside ourselves, yet applied to ourselves―Almighty power, yet utilized for insignificant “me.” “I can do all things” ―yet not in self-power, but “through Christ, who strengtheneth me.” Let the believer say, “By God’s grace I will live and do in the power of my risen Lord.”
Such as boast of their spiritual attainments have not attained to boasting in Christ. The highest spiritual attainment is to make all of Christ. The Christian has power to overcome in the battle of life― “yet not I”; he has patience to suffer― “yet not I”; grace to die― “yet not I.” And when at length he is ushered into the Father’s presence, and beholds the King in His beauty, still he will rejoice― “yet not I,” but that all is of Christ.