Jesus beatifies mourning, not moping. He does not counsel the long face. He does, however, bless real sadness, a state that can as easily coexist with an outwardly happy life as do all the other normal contradictions of living. (The deepest joy may reside in persons with the deepest sadness.)

Sadness and joy are not mutually exclusive; they are often cause and effect. (Much folk music lives from this strange but strong combination.) Jesus lends his authority to the perception that it is those for whom sadness is deep that God is real.

from The Christbook