Happiness depends on good happenings to us. It is fleeting and elusive. Joy, on the other hand, is the attitude of delight based on the nature of God. It is constant as God is constant. Speaking theologically, John MacArthur defined joy as a gift from God (Ps. 16:11; Lk. 2:10) to those who believe (Rom. 14:17; Gal. 5:22) and receive His Word (Jer. 15:16; 1 Jn. 1:4) mixed with trials (1 Thess 1:6) and hope for future glory (Jude 24). No wonder scripture says to the believer, “rejoice always” (1 Thess. 5:16-18) and “count it all joy” (Ja. 1:2).
Joy is excited when we fix our thoughts on the unchanging goodness of God toward us.