Complete Commentary on the Whole Bible, by Matthew Henry, at sacred-texts.com
(Psa 3:1-3) David complains to God of his enemies, and confides in God.
(Psa 3:4-8) He triumphs over his fears, and gives God the glory, and takes to himself the comfort.
An active believer, the more he is beaten off from God, either by the rebukes of providence, or the reproaches of enemies, the faster hold he will take, and the closer will he cleave to him. A child of God startles at the very thought of despairing of help in God. See what God is to his people, what he will be, what they have found him, what David found in him. 1. Safety; a shield for me; which denotes the advantage of that protection. 2. Honour; those whom God owns for his, have true honour put upon them. 3. Joy and deliverance. If, in the worst of times, God's people can lift up their heads with joy, knowing that all shall work for good to them, they will own God as giving them both cause and hearts to rejoice.
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.