He is like to a man. Heavenly doctrine is indeed a mirror in which God presents himself to our view; but so that we may be transformed unto his image, as Paul says in 2-Corinthians 3:18. But here he speaks of the external glance of the eye, not of the vivid and efficacious meditation which penetrates into the heart. It is a striking comparison, by which he briefly intimates, that a doctrine merely heard and not received inwardly into the heart avails nothing, because it soon vanishes away.

For if any be - The ground of the comparison in these verses is obvious. The apostle refers to what all persons experience, the fact that we do not retain a distinct impression of ourselves after we have looked in a mirror. While actually looking in the mirror, we see all our features, and can trace them distinctly; when we turn away, the image and the impression both vanish. When looking in the mirror, we can see all the defects and blemishes of our person; if there is a scar, a deformity, a feature of ugliness, it is distinctly before the mind; but when we turn away, that is "out of sight and out of mind." When unseen it gives no uneasiness, and, even if capable of correction, we take no pains to remove it. So when we hear the word of God. It is like a mirror held up before us. In the perfect precepts of the law, and the perfect requirements of the gospel, we see our own short-comings and defects, and perhaps think that we will correct them. But we turn away immediately, and forget it all. If, however, we were doers of the word," we should endeavor to remove all those defects and blemishes in our moral character, and to bring our whole souls into conformity with what the law and the gospel require. The phrase "natural face" (Greek: face of birth), means, the face or appearance which we have in virtue of our natural birth. The word glass here means mirror. Glass was not commonly used for mirrors among the ancients, but they were made of polished plates of metal. See the Isaiah 3:24 note, and Job 37:18 note.

Beholding his natural face in a glass - This metaphor is very simple, but very expressive. A man wishes to see his own face, and how, in its natural state, it appears; for this purpose he looks into a mirror, by which his real face, with all its blemishes and imperfections, is exhibited. He is affected with his own appearance; he sees deformities that might be remedied; spots, superfluities, and impurities, that might be removed. While he continues to look into the mirror he is affected, and wishes himself different to what he appears, and forms purposes of doing what he can to render his countenance agreeable. On going away he soon forgets what manner of person he was, because the mirror is now removed, and his face is no longer reflected to himself; and he no longer recollects how disagreeable he appeared, and his own resolutions of improving his countenance. The doctrines of God, faithfully preached, are such a mirror; he who hears cannot help discovering his own character, and being affected with his own deformity; he sorrows, and purposes amendment; but when the preaching is over, the mirror is removed, and not being careful to examine the records of his salvation, the perfect law of liberty, James 1:25, or not continuing to look therein, he soon forgets what manner of man he was; or, reposing some unscriptural trust in God's mercy, he reasons himself out of the necessity of repentance and amendment of life, and thus deceives his soul.

(17) For if any be a hearer of the word, and not a doer, he is like unto a man beholding his (u) natural face in a glass:
(17) Secondly: because they lose the most important use of God's word, if they do not use it to correct the faults that they know.
(u) He alludes to that natural stain, which is contrary to the purity that we are born again into, the living image which we see in the law.

But if any man be a hearer of the word, and not a doer,.... The Arabic version here again reads, "a hearer of the law", and so some copies; not hearing, but practice, is the main thing; not theory, but action: hence, says R. Simeon, not the word, or the searching into it, and the explanation of it, is the root, or principal thing, , "but the work" (p): and if a man is only a preacher, or a hearer, and not a doer,
he is like unto a man beholding his natural face in a glass; or, "the face of his generation"; the face with which he was born; his true, genuine, native face; in distinction from any counterfeit one, or from the face of his mind: it means his own corporeal face. The Ethiopic version renders it, "the lineaments of his face".
(p) Pirke Abot, c. 1. sect. 17.

For--the logical self-deceit (James 1:22) illustrated.
not a doer--more literally, "a notdoer" [ALFORD]. The true disciple, say the rabbis, learns in order that he may do, not in order that he may merely know or teach.
his natural face--literally, "the countenance of his birth": the face he was born with. As a man may behold his natural face in a mirror, so the hearer may perceive his moral visage in God's Word. This faithful portraiture of man's soul in Scripture, is the strongest proof of the truth of the latter. In it, too, we see mirrored God's glory, as well as our natural vileness.

Beholding his face in a glass - How exactly does the scripture glass show a man the face of his soul!