John Calvin on James 1:23-24

23 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.