Proverbs 15:13

A merry heart maketh a cheerful countenance
Or, a "joyful heart" ^F3; that is joyful in the God of its salvation; that rejoices in Christ Jesus; is filled with joy and peace through believing in him, in his person, blood, righteousness, and sacrifice; that has a comfortable view of his justification by his righteousness, of peace and pardon by his blood, of the atonement of his sins by his sacrifice; to whom he has said, "be of good cheer, thy sins are forgiven thee", ( Matthew 9:2 ) ; who has peace in him, though tribulation in the world: as such a man's heart must be made glad, this will make his countenance cheerful, or cause him to lift up his head with joy; as it is in natural things, so it is in spiritual ones; but by sorrow of the heart the spirit is broken;
a man is dejected, his spirits sink, and it is seen in his countenance: there is a great sympathy between the body and mind, the one is much affected by the other; when the heart is full of sorrow, the animal spirits are low, the nerves are loosened, the whole frame, of nature is enfeebled, and the body emaciated; this is often the case through outward troubles {d}: physicians say ^F5 that grief weakens the strength, and destroys the spirits, more than labour does. "The sorrow of the world worketh death", ( 2 Corinthians 7:10 ) ; and sometimes, through spiritual troubles, a sense of sin and guilt of it, a legal sorrow, which produces a legal contrition of spirit; and such "a wounded spirit who can bear?" ( Proverbs 18:14 ) . This is the effect of a mere work of the law upon the conscience; and stands opposed to the spiritual joy, and the effects of it, the Gospel brings.