According to the usage of the Hebrews, these words, which are in the past tense, I laid me down and slept, are taken sometimes for the future, I will lie down and sleep. If we retain the reading of the verb in the past tense, David expresses a wonderful and almost incredible steadfastness of mind in that he slept so soundly in the midst of many deaths, as if he had been beyond the reach of all danger. He had doubtless been tossed amidst the merciless waves of anxiety, but it is certain their violence had been allayed by means of faith, so that however much he was disquieted, he reposed in God. Thus the godly never fail in ultimately proving victorious over all their fears, whereas the ungodly, who do not rely upon God, are overwhelmed with despair, even when they meet with the smallest perils. Some think there is here a change of tenses; and, therefore, translate the verbs into the fixture tense, I will lay me down and will sleep, and will awake, because immediately after a verb of the future is subjoined, The Lord shall uphold me But as he expresses, by these last words, a continuous act, I thought it unnecessary to change the tenses in the three first verbs. Still we ought to know, that this confidence of safety is not to be referred peculiarly to the time of his affliction, or, at least, is not to be limited to it: for, in my judgment, David rather declares how much good he had obtained by means of faith and prayer; namely the peaceful and undisturbed state of a well regulated mind. This he expresses metaphorically when he says, that he did the ordinary actions of life without being disturbed by fear. "I have not lain," says he, "waking and restless on my bed; but I have slept soundly, whereas such manner of sleeping does not generally happen to those who are full of thought and fear." But let us particularly notice that David came to have this confidence of safety from the protection of God, and not from stupidity of mind. Even the wicked are kept fast asleep through an intoxication of mind, while they dream of having made a covenant with death. It was otherwise with David, who found rest on no other ground but because he was upheld by the power of God, and defended by his help. In the next verse, he enlarges upon the incalculable efficacy of this confidence, of which all the godly have some understanding, from their experience of the divine protection. As the power of God is infinite, so they conclude that it shall be invincible against all the assaults, outrages, preparations, and forces of the whole world. And, indeed, unless we ascribe this honor to God, our courage shall be always failing us. Let us, therefore, learn, when in dangers, not to measure the assistance of God after the manner of man, but to despise whatever terrors may stand in our way, inasmuch as all the attempts which men may make against God, are of little or no account.

I laid me down and slept - Notwithstanding these troubles and dangers I had such confidence that God hears prayer, and such calm trust in his protection, that I laid me down gently and slept securely. The psalmist mentions this as a remarkable proof of the divine protection and favor. He was driven from his capital, his throne, and his home. He was compelled to wander as a poor fugitive, accompanied by only a few friends. He was pursued by enemies, who were numbered by thousands. He was made an exile, and persecuted by his own son; and with this son there were men of age and of experience in war. The forces of his enemies might come upon him at any moment. In these circumstances, persecuted as he was, and under all the anxiety and distress which he felt in view of the ungrateful conduct of his own son, he regarded it as a singular proof of the divine favor, and as an illustration of the peace which confidence in God gives to those who put their trust in him, that on such a dreadful night he was permitted to lie calmly down and sleep. As such a proof and illustration it may be regarded here: a proof of the unspeakable value of the divine favor, and an illustration of the effect of confidence in God in giving calmness and peace of mind in time of trouble. Psalm 127:2.
I awaked - Still safe and secure. He had not been suddenly attacked by his foes, and made to sleep the sleep of death; he had not been crushed by anguish of spirit. That we are "awaked" in the morning after a night's refreshing slumber; that we are raised up again to the enjoyments of life; that we are permitted again to greet our friends and to unite with them in the privileges of devotion, should always be regarded as a new proof of the goodness of God, and should lead to acts of praise. We have no power to awake ourselves; and when we remember how many are taken away from our world each night - how many there are who lie down to sleep to wake no more, we should never rise from a bed of repose without giving our first thoughts in gratitude to our Great Preserver.
For the Lord sustained me - He kept me from danger; he preserved me from death. And it is as true now as it was then, that God is the supporter of life when men sleep. He guards us; he causes the action of the heart to be continued as it propels the blood through our frame; he secures the gentle heaving of the lungs, both when we slumber and when we wake.

I laid me down and slept - He who knows that he has God for his Protector may go quietly and confidently to his bed, not fearing the violence of the fire, the edge of the sword, the designs of wicked men, nor the influence of malevolent spirits.
I awaked - Though humanly speaking there was reason to fear I should have been murdered in my bed, as my most confidential servants had been corrupted by my rebellious son; yet God, my shield, protected me. I both slept and awaked; and my life is still whole in me.

I laid me down and slept,.... After the battle was over between Absalom's men and his, says Aben Ezra; but rather this was in the midst of his trouble and distress, since he afterwards prays for salvation: and this sleep was either, as Jarchi observes, through his heart being overwhelmed with grief; for there have been instances of persons sleeping through sorrow, as Elijah, Jonah, and the disciples of Christ, 1-Kings 19:4; or rather this is expressive of the calmness and serenity of his mind amidst his troubles; he laid himself down in peace, and slept quietly and comfortably; he did not lose a night's rest, his sleep was sweet unto him; which was a blessing of life from the Lord that everyone does not enjoy; see Psalm 127:2;
I awakened; in the morning, alive and cheerful, Some lay themselves down and never awake more, as Sisera the captain of Jabin's army, and Ishbosheth the son of Saul; and this might have been David's case, considering the circumstances he was in: and others, through perplexing thoughts and cares, or pains of body, or uneasy dreams, rise fatigued and distressed; but David arose in good health of body, and tranquillity of mind, and comfortably refreshed;
for the Lord sustained me; the psalmist committed himself to the care and protection of God; he laid himself down in his arms, and there slept in safety; the Lord preserved him, who is Israel's keeper, that neither slumbers nor sleeps: and he rose in health and cheerfulness in the morning, supported by his right hand. This shows, that lying down to sleep, when in such circumstances, and awaking with cheerfulness, were not owing to rashness, stupidity, and insensibility, but to divine supports. These words may be interpreted, as they are by some of the ancients, of the death of Christ, and of his resurrection from the dead by the power of God; death is often expressed by sleep, and the resurrection of the dead by an awaking out of sleep, Daniel 12:2; and Christ's death being signified by lying down and sleeping, may denote both the voluntariness of it, that he laid down his life freely and willingly; and his short continuance under the power of death, it was but like a night's sleep; and his resurrection from the dead, being expressed by an awaking through the Lord's sustaining him, shows that it was by the power of God, even the exceeding greatness of his power: and the whole of this may be applied to the case and state of the saints and people of God, who at times have rest and peace amidst their enemies; though they have tribulation in the world, they have peace in Christ; and notwithstanding the temptations of Satan, and the corruptions of their own hearts, they have joy and comfort through believing in Christ; the Lord sustains them with precious promises, and supports them with the discoveries of his love, and upholds them with the right hand of his righteousness.

the Lord sustained me--literally, "will sustain me," as if his language or thought when he laid down, and the reason of his composure.

(Hebrews.: 3:6-7) That this God will protect him, His protection during the past night is now a pledge to him in the early morning. It is a violation of the rules of grammar to translate ואישׁנה: I shall go to sleep, or: I am going to sleep. The 1 pers. fut. consec. which is indicated by the ו, is fond of taking an ah of direction, which gives subjective intensity to the idea of sequence: "and thus I then fell asleep," cf. Psalm 7:5; Psalm 119:55, and frequently, Genesis 32:6, and more especially so in the later style, Ezra 9:3; Nehemiah 13:21, vid., Ges. 49, 2, Bttcher, Neue Aehrenlese, No. 412. It is a retrospective glance at the past night. Awaking in health and safety, he feels grateful to Him to whom he owes it: יהוה יסמכני. It is the result of the fact that Jahve supports him, and that God's hand is his pillow.
(Note: Referred to the other David, Psalm 3:6 has become an Easter-morning call, vid., Val. Herberger's Paradies-Blmlein aus dem Lustgarten der Psalmen (Neue Ausg. 1857) S. 25.)
Because this loving, almighty hand is beneath his head (Song 2:6) he is inaccessible and therefore also devoid of fear. שׁית (שׁוּת) carries its object in itself: to take up one's position, as in Isaiah 22:7, synon. חנה Psalm 28:3 and שׂים 1-Kings 20:12, cf. ἐπιτιθέναι τινί. David does not put a merely possible case. All Israel, that is to say ten thousands, myriads, were gone over to Absolom. Here, at the close of the third strophe, סלה is wanting because the לא אירא (I will not fear) is not uttered in a tone of triumph, but is only a quiet, meek expression of believing confidence. If the instruments struck up boldly and suddenly here, then a cry for help, urged forth by the difficulties that still continually surrounded him, would not be able to follow.

Slept - Securely, casting all my cares upon God. Awaked - After a sweet and undisturbed sleep.