For what man knoweth? Two different things he intends to teach here: first, that the doctrine of the Gospel cannot be understood otherwise than by the testimony of the Holy Spirit; and secondly, that those who have a testimony of this nature from the Holy Spirit, have an assurance as firm and solid, as if they felt with their hands what they believe, for the Spirit is a faithful and indubitable witness. This he proves by a similitude drawn from our own spirit: for every one is conscious of his own thoughts, and on the other hand what lies hid in any man's heart, is unknown to another. In the same way what is the counsel of God, and what his will, is hid from all mankind, for "who hath been his counselor?" (Romans 11:34.) It is, therefore, a secret recess, inaccessible to mankind; but, if the Spirit of God himself introduces us into it, or in other words, makes us acquainted with those things that are otherwise hid from our view, there will then be no more ground for hesitation, for nothing that is in God escapes the notice of the Spirit of God. This similitude, however, may seem to be not altogether very appropriate, for as the tongue bears an impress of the mind, mankind communicate their dispositions to each other, so that they become acquainted with each other's thoughts. Why then may we not understand from the word of God what is his will? For while mankind by pretenses and falsehoods in many cases conceal their thoughts rather than discover them, this cannot happen with God, whose word is undoubted truth, and his genuine and lively image. We must, however, carefully observe how far Paul designed to extend this comparison. A man's innermost thought, of which others are ignorant, is perceived by himself alone: if he afterwards makes it known to others, this does not hinder but that his spirit alone knows what is in him. For it may happen that he does not persuade: it may even happen that he does not properly express his own meaning; but even if he attains both objects, this statement is not at variance with the other -- that his own spirit alone has the true knowledge of it. There is this difference, however, between God's thoughts and those of men, that men mutually understand each other; but the word of God is a kind of hidden wisdom, the loftiness of which is not reached by the weakness of the human intellect. Thus the light shineth in darkness, (John 1:5,) aye and until the Spirit opens the eyes of the blind. The spirit of a man Observe, that the spirit of a man is taken here for the soul, in which the intellectual faculty, as it is called, resides. For Paul would have expressed himself inaccurately if he had ascribed this knowledge to man's intellect, or in other words, the faculty itself, and not to the soul, which is endued with the power of understanding.

For what man - The design of this is, to illustrate what he had just said by a reference to the way in which man acquires the knowledge of himself. The purpose is to show that the Spirit has an exact and thorough knowledge of the things of God; and this is done by the very striking thought that no man can know his own mind, his own plans and intentions, but himself - his own spirit. The essential idea is, that no man can know another; that his thoughts and designs can only be known by himself, or by his own spirit; and that unless he chooses to reveal them to others, they cannot ascertain them. So of God. No man can penetrate his designs; and unless he chooses to make them known by his Spirit, they must forever remain inscrutable to human view.
The things of a man - The "deep things" - the hidden counsels, thoughts, plans, intentions.
Save the spirit of man - Except his own mind; that is, himself. No other man can fully know them. By the spirit of man here, Paul designs to denote the human soul - or the intellect of man. It is not to be supposed that he here intends to convey the idea that there is a perfect resemblance between the relation which the soul of man bears to the man, and the relation which the Holy Spirit bears to God. The illustration is to be taken in regard to the point immediately before him - which is, that no one could know and communicate the deep thoughts and plans of God except his Spirit - just as no one could penetrate into the intentions of a man, and fully know them, but himself. The passage proves, therefore, that there is a knowledge which the Spirit has of God, which no man, no angel can obtain, just as every man's spirit has a knowledge of his own plans which no other man can obtain; that the Spirit of God can communicate his plans and deep designs, just as a man can communicate his own intentions; and consequently, that while there is a distinction of some kind between the Spirit of God and God, as there is a distinction which makes it proper to say that a man has an intelligent soul, yet there is such a profound and intimate knowledge of God by the Spirit, that he must be equal with him; and such an intimate union, that he can be called "the Spirit of God," and be one with God, as the human soul can be called "the spirit of the man," and be one with him.
In all respects we are not to suppose that there is a similarity. In these points there is - It may be added that the union, the oneness of the Spirit of God with God, is no more absurd or inexplicable than the union of the spirit of man with the man; or the oneness of the complex person made up of body and soul, which we call man. When people have explained all the difficulties about themselves - in regard to their own bodies and spirits, it will be time to advance objections against the doctrines here stated in regard to God.
Even so - To the same extent; in like manner.
The things of God - His deep purposes and plans.
Knoweth no man - Man cannot search into them - any more than one man can search the intentions of another.

For what man knoweth the things of a man - The word ανθρωπων in the first clause is omitted by the Codex Alexandrinus, and one other; and by Athanasius, Cyril, and Vigil of Tapsus. Bishop Pearce contends strongly against the authenticity of the word, and reads the passage thus: "For what is there that knoweth the things of a man, except the spirit of a man that is in him?" "I leave out," says the learned bishop, "ανθρωπων, with the Alexandrian MS., and read τις γαρ οιδεν τα του ανθρωπου; because I conceive that the common reading is wide of St. Paul's meaning; for to say, What man except the spirit of a man, is (I think) to speak improperly, and to suppose that the spirit of a man is a man; but it is very proper to say, What except the spirit of a man: τις is feminine as well as masculine, and therefore may be supplied with ουσια, or some such word, as well as with ανθρωπος." Though the authority for omitting this word is comparatively slender, yet it must be owned that its omission renders the text much more intelligible. But even one MS. may preserve the true reading.
The spirit of a man knows the things of a man: that is, a man is conscious of all the schemes, plans, and purposes, that pass in his own mind; and no man can know these things but himself. So, the Spirit of God, He whom we call the Third Person of the glorious Trinity, knows all the counsels and determinations of the Supreme Being. As the Spirit is here represented to live in God as the soul lives in the body of a man, and as this Spirit knows all the things of God, and had revealed those to the apostles which concern the salvation of the world, therefore what they spoke and preached was true, and men may implicitly depend upon it. The miracles which they did, in the name of Christ, were the proof that they had that Spirit, and spoke the truth of God.

(10) For what man knoweth the things of a man, save the (l) spirit of man which is in him? even so the things of God knoweth no man, but the Spirit of God.
(10) He sets it forth in comparison, which he spoke by the inspiration of the Sprit. As the power of man's intellect searches out things pertaining to man, so does our mind by the power of the Holy Spirit understand heavenly things.
(l) The mind of man which is endued with the ability to understand and judge.

For what man knoweth the things of a man,.... The thoughts of a man's heart, the conceptions of his mind, the schemes he is drawing there, his designs, purposes, and intentions; these can never be known by another man, no, nor by angels or devils; not by any creature; by none
save the spirit of a man which is in him? which is only conscious to, and can only make known the things that are in him:
even so the things of God knoweth no man, but the Spirit of God; and which, as it proves how secret, hidden, unknown, the mysteries of grace are, until revealed by the Spirit; so it gives full evidence to the deity of the Holy Ghost, and clearly shows he must be God, who is in him, knows the thoughts of his heart, the counsels of his mind, his purposes and decrees, and what is contained in them.

what man, &c.--literally, "who of men knoweth the things of a man, save the spirit of that man?"
things of God knoweth no man--rather, "none knoweth," not angel or man. This proves the impossibility of any knowing the things of God, save by the Spirit of God (who alone knows them, since even in the case of man, so infinitely inferior in mind to God, none of his fellow men, but his own spirit alone knows the things hidden within him).

For what man knoweth the things of a man - All the inmost recesses of his mind; although men are all of one nature, and so may the more easily know one another. So the things of God knoweth no one but the Spirit - Who, consequently, is God.