Happiness, 
experiencing total well-being, 
is the gift of God's grace granted to those
(1) who live in God's presence(Ps.84:4), 
(2) who are not ultimately self-reliant but who find in God the source of their strength(84:5), and

(3) who live a life of faith in God(84:12).

(Mark D. Futato, "The Book of Psalms")