11. 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.