"Because it is so supremely intimate to oneself yet also intimately related to an other, joy is a reality best understood in the “middle voice”— that is, a reality that is not purely passive, happening to us, nor simply active, something we do; but partaking of both receptivity and dynamism. Other, equally significant phenomena in Christian life are also framed in the middle voice; the Koine word for feeling compassion is σπλαγχνίζοµαι (splagchnizomai), which is another crucial “action” that is in the middle voice; and a similar thing can be said of ελθών (elthon) “to arrive” or “to come”, which is used for the Prodigal Son’s recognition, amidst the swine, of the reality to which his life has come (of longing for the quality of life of pigs). Hence human agency may be implicated in the achievement of joy in a slightly less indirect way than it can be in the attainment of happiness, which may be why St. Paul repeatedly exhorts people to be joyful (not happy)—e.g. Philippians 4:4 “Rejoice in the Lord always; and I say again, rejoice.")
Thus understood as an excess rapture, catching us up into a reality in the “middle
voice,” joy is a sort of sacramental state: in Creation yet prompted ultimately by
something beyond and before Creation, a reality simultaneously speaking of immediacy
and transcendence, something done to you yet something you manifest, express, realize
and participate in. Here and there, now and not yet, you and another, creation and
Creator—joy can serve as a synechdoche of the Christian life as a whole.
Charles Mathewes, "Toward a Theology of Joy" (2014).