"O send out Thy light and Thy truth: let them lead me; let them bring me unto Thy holy hill, and to Thy tabernacles. Then will I go unto the altar of God, unto God my exceeding joy: yea, upon the harp will I praise Thee, O God my God" (Psalm 43:3-4).
God could only be David's "exceeding joy" if He is himself exceedingly joyful.
He is, and the Biblical understanding of our Lord as a being of inestimable joy is life changing. "The joy of the Lord is your strength" declared Nehemiah to the children of Israel, and this is even more true of the born again believer in the Lord Jesus Christ who is indwelt by the Holy Spirit. "The fruit of the Spirit is... joy" (Galatians 5:22). We must perceive God in such sublime terms because otherwise we do not know Him rightly, and otherwise we will not be the joyful reflections of His exultant heart.
This does not preclude the sensibilities that we sometimes more readily perceive in God. He grieves and mourns. He can be displeased and angered, and profound sorrow beyond any sadness we have ever known is depicted by Scripture concerning our Lord. However, joy is the prevailing atmosphere of the Divine heart, and knowing "God my exceeding joy" in the depths of His Person will fill the depths of our own with "joy unspeakable and full of glory" (I Peter 1:8).
The basis of joy in God is the triune being of Father, Son, and Holy Spirit. Three perfect Persons dwelling in perfect Oneness and in perfect love comprises the very essence of joy. Indeed, joy in us is always the expression of the joy of God revealed in us. From everlasting to everlasting, the Father, the Son, and the Holy Spirit have rejoiced in each other, and in this "moment" of their existence, we can be sure that the Divine cup runs over with holy and immeasurable exultation.
Again, we must know God in these terms of joy. Nehemiah promised that this is our strength, and nothing will more fill our hearts with empowering joy than gazing into our Lord's heart and discovering that He is Himself the very essence of triune joy. A long eternity awaits our thrilled beholding of such glory, and this lifetime, this day, and this moment offer to us the gaze that will thrill us and fill us, causing our own cups to overflow with abundant excess of joy unspeakable and full of glory.
"But unto the Son He saith, Thy throne, O God, is for ever and ever: a scepter of righteousness is the scepter of Thy kingdom. Thou hast loved righteousness, and hated iniquity; therefore God, even Thy God, hath anointed Thee with the oil of gladness above thy fellows."
"Rejoice in the Lord alway, and again I say, rejoice."