The Joy of Jesus is Joy itself

We profit from the Word when we perceive that joy is a duty. "Rejoice in the Lord alway: and again I say, Rejoice" (Phil. 4:4). The Holy Spirit here speaks of rejoicing as a personal, present and permanent duty for the people of God to carry out. The Lord has not left it to our option whether we should be glad or sad, but has made happiness an obligation. Not to rejoice is a sin of omission. Next time you meet with a radiant Christian, do not chide him, ye dwellers in Doubting Castle, but chide yourselves; instead of being ready to call into question the Divine spring of his mirth, judge yourself for your doleful state.
It is not a carnal joy which we are here urging, by which we mean a joy which comes from carnal sources. It is useless to seek joy in earthly riches, for frequently they take to themselves wings and fly away. Some seek their joy in the family circle, but that remains entire for only a few years at most. No, if we are to "rejoice evermore" it must be in an object that lasts for evermore. Nor is it a fanatical joy we have reference to. There are some with an excitable nature who are happy only when they are half out of their minds; but terrible is the reaction. No, it is an intelligent, steady, heart delight in God Himself. Every attribute of God, when contemplated by faith, will make the heart sing. Every doctrine of the Gospel, when truly apprehended, will call forth gladness and praise.