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.