3:4-8 Care and grief do us good, when they engage us to pray to God, as in earnest. David had always found God ready to answer his prayers. Nothing can fix a gulf between the communications of God's grace towards us, and the working of his grace in us; between his favour and our faith. He had always been very safe under the Divine protection. This is applicable to the common mercies of every night, for which we ought to give thanks every morning. Many lie down, and cannot sleep, through pain of body, or anguish of mind, or the continual alarms of fear in the night. But it seems here rather to be meant of the calmness of David's spirit, in the midst of his dangers. The Lord, by his grace and the consolations of his Spirit, made him easy. It is a great mercy, when we are in trouble, to have our minds stayed upon God. Behold the Son of David composing himself to his rest upon the cross, that bed of sorrows; commending his Spirit into the Father's hands in full confidence of a joyful resurrection. Behold this, O Christian: let faith teach thee how to sleep, and how to die; while it assures thee that as sleep is a short death, so death is only a longer sleep; the same God watches over thee, in thy bed and in thy grave. David's faith became triumphant. He began the psalm with complaints of the strength and malice of his enemies; but concludes with rejoicing in the power and grace of his God, and now sees more with him than against him. Salvation belongeth unto the Lord; he has power to save, be the danger ever so great. All that have the Lord for their God, are sure of salvation; for he who is their God, is the God of Salvation.

7. Arise, O Lord—God is figuratively represented as asleep to denote His apparent indifference (Ps 7:6). The use of "cheekbone" and "teeth" represents his enemies as fierce, like wild beasts ready to devour (Ps 27:2), and smiting their cheekbone (1Ki 22:24) denotes violence and insult.

thou hast broken—God took his part, utterly depriving the enemy of power to injure.