What is man - What claim has one so weak, and frail, and short-lived, to be remembered by time? What is there in man that entitles him to so much notice? Why has God conferred on him so signal honor? Why has he placed him over the works of his hands? Why has he made so many arrangements for his comfort? Why has he done so much to save him? He is so insignificant his life is so much like a vapor, he so soon disappears, he is so sinful and polluted, that the question may well be asked, why such honor has been conferred on him, and why such a dominion over the world has been given him. See these thoughts more fully expanded in the notes at Hebrews 2:6.
That thou art mindful of him - That thou dost remember him; that is, think of him, attend to him - that he does not pass away wholly from thy thoughts. Why should a God who is so vast and glorious, and who has all the starry worlds, so beautiful and grand, to claim his attention - why should he turn his thoughts on man? And especially why should he honor him as he has done by giving him dominion over the works of his hands?
And the son of man - Any descendant of man - any one of the race. What was man, as he was originally made, that such exalted honor should have been conferred on him; and what has any one of his descendants become, in virtue of his native faculties or acquired endowments, that he should be thus honored? The design is the same as in the former part of the verse, to express the idea that there was nothing in man, considered in any respect, that entitled him to this exalted honor. Nothing that man has done since the time when the question was asked by the psalmist has contributed to diminish the force of the inquiry.
That thou visitest him - As thou dost; that is, with the attention and care which thou dost bestow upon him; not forgetting him; not leaving him; not passing him by. The word used here - פקד pâqad - would properly express a visitation for any purpose - for inspection, for mercy; for friendship, for judgment, etc. Here it refers to the attention bestowed by God on man in conferring on him such marks of favor and honor as he had done - such attention that he never seemed to forget him, but was constantly coming to him with some new proof of favor. What God has done for man since the psalmist wrote this, has done nothing to weaken the force of this inquiry.

What is man - מה אנוש mah enosh, what is wretched, miserable man; man in his fallen state, full of infirmity, ignorance, and sin?
That thou art mindful of him? - That thou settest thy heart upon him, keepest him continually in thy merciful view.
And the son of man - ובן אדם uben Adam, and the son of Adam, the first great rebel; the fallen child of a fallen parent. See the note on Job 7:17. Some think eminent men are here intended. What is man in common; what the most eminent men; that thou shouldst be mindful of them, or deign to visit them?
That thou visitest him? - By sending thy Holy Spirit to convince him of sin, righteousness, and judgment. It is by these visits that man is preserved in a salvable state. Were God to withhold them, there would be nothing in the soul of man but sin, darkness, hardness, corruption, and death.

Quid est homo quod memor es ejus; aut filius hominis, quoniam visitas eum?
Trans. What es man that thu ert menand of hym: or son of man for thou visites hym?
Par. Als it war with despyte, he sais "man", erdely and synful, qwat es he, that thu has mynd of hym. Als fer sett fra the; at the lest gyfand hym hele and ese of body. Or "son of man": that es, he that es gastely, and beres the ymage of heven. Qwat es he, for thou visits hym. Als present the qwilk es nere the for clennes of lyf. Or "son of man" he calles Crist, thrugh qwam he visits mannes kynd.

What is (b) man, that thou art mindful of him? and the son of man, that thou visitest him?
(b) It was sufficient for him to have set forth his glory by the heavens, though he had not come so low as to man who is but dust.

What is man, that thou art mindful of him?.... That is, the psalmist, while he was considering the greatness and glory of the celestial bodies, thought this within himself, and so expressed it; which is to be understood, not of man in general, nor of Adam in a state of innocence; he could not be called "Enosh", the word here used, which signifies a frail, weak, sickly mortal man; nor could he with any propriety be said to be the son of man, as in the following clause: nor of fallen man, or of Adam's posterity, descending from him by ordinary generation; for all things are not put in subjection to them, as is hereafter said of man: but this is to be understood of the man Christ Jesus, as it is interpreted in Hebrews 2:6; or of that individual of human nature which Christ assumed. The name of Enosh well agrees with him, who was a man of no note and esteem among men, a worm and no man, a man of sorrows and acquainted with griefs, encompassed with infirmities, and was subject to death, and did die. Now it was a marvellous thing that God should be mindful of that individual of human nature; that he should prepare it in his council and covenant; that among the vast numbers of individuals which it came up in his infinite mind to create, he should choose this, to exalt it, and appoint it to union with his own Son, and take that delight in it he did; that when it was formed by his Spirit, he should anoint it with the oil of gladness above his fellows; that he should take such providential care of it, and so often and so strongly express his affection for it; that he should regard it, and support it under sufferings; and when in the grave, did not leave it, nor suffer it to see corruption; but raised it from the dead, and gave it glory, and exalted it at his own right hand;
and the son of man, that thou visitest him? The name of "the son of man" is the name of the Messiah, in Psalm 80:17; and is often given to Christ, and used by him of himself in the New Testament. And this visiting of him is not to be understood in a way of wrath, though he was so visited by God, when he bore the chastisements of his people; but in a way of favour, by bestowing upon him without measure the gifts and graces of his Spirit; by affording him his gracious presence, and tilling him with spiritual peace and joy.

man--literally, "frail man," an allusion to his essential infirmity.
son of man--only varies the form of speech.
visitest--in favor (Psalm 65:10). This favor is now more fully illustrated.

What is man - How mean and inconsiderable a thing is man, if compared with thy glorious majesty. Man - Hebrews. infirm, or miserable man. By which it is apparent that he speaks of man, not according to the state of his creation, but as fallen into a state of sin and misery, and mortality. Mindful - Carest for him, and conferest such high favours upon him. The son - Hebrews. the son of Adam, that great apostate from God, the sinful son of a sinful father, his son by likeness of disposition and manners, no less than by procreation. All which tends to magnify the following mercy. Visitest - Not in anger, as that word is sometimes used, but with thy grace and mercy.