And thus are the secrets of his heart - As these, who were the prophets or teachers, had often the discernment of spirits, they were able in certain cases, and probably very frequently, to tell a man the secrets of his own heart; and, where this was not directly the case, God often led his ministers to speak those things that were suitable to the case before them, though they themselves had no particular design. The sinner, therefore, convinced that God alone could uncover the secrets of his heart, would be often obliged to fall down on his face, abashed and confounded, and acknowledge that God was truly among them. This seems to be the plain meaning of the passages before us.
And thus are the secrets of his heart made manifest - Made manifest to himself in a surprising and remarkable manner. He shall be led to see the “real” designs and motives of his heart. His conscience would be awakened; he would recall his former course of life; he would see that it was evil; and the present state of his heart would be made known to himself. It is possible that he would “suppose that the speaker was aiming directly at him, and “revealing” his feelings to others; for such an effect is often produced. The convicted sinner often supposes that the preacher particularly intends “him,” and wonders that he has such an acquaintance with his feelings and his life; and often supposes that he is designing to disclose his feelings to the congregation. It is possible that Paul here may mean that the prophets, by inspiration, would be able to reveal some secret facts in regard to the stranger; or to state the ill design which he might have had in coming into the assembly; or to state some things in regard to him which could be known only to himself; as was the case with Ananias and Sapphira (Acts 5:1, seq.); but perhaps it is better to understand this in a more general sense, as describing the proper and more common effect of truth, when it is applied by a man‘s own conscience. Such effects are often witnessed now; and such effects show the truth of religion; its adaptedness to people; the omniscience and the power of God; the design of the conscience, and its use in the conversion of sinners.
And so falling down on his face - The usual posture of worship or reverence in eastern countries. It was performed by sinking on the knees and hands, and then placing the face on the ground. This might be done publicly; or the apostle may mean to say that it would lead him to do it in private.
He will worship God - He will be converted, and become a Christian.
And report that God - Will become your friend, and an advocate for the Christian religion. An enemy will be turned to a friend. Doubtless this was often done. It is now often done. Paul‘s argument is, that they should so conduct their public devotions as that they should be adapted to produce this result.