But whoso looketh - (παρακύψας parakupsas). This word means, to stoop down near by anything; to bend forward near, so as to look at anything more closely. See the word explained in the notes at 1 Peter 1:12. The idea here is that of a close and attentive observation. The object is not to contrast the manner of looking in the glass, and in the law of liberty, implying that the former was a “careless beholding,” and the latter an attentive and careful looking, as Doddridge, Rosenmuller, Bloomfield, and others suppose; for the word used in the former case (κατενόησε katanoēse) implies intense or accurate observation, as really as the word used here; but the object is to show that if a man would attentively look into, and continue in the law of liberty, and not do as one who went away and forgot how he looked, he would be blessed. The emphasis is not in the manner of looking, it is on the duty of continuing or persevering in the observance of the law.
The perfect law of liberty - Referring to the law of God or his will, however made known, as the correct standard of conduct. It is called the perfect law, as being wholly free from all defects; being just such as a law ought to be. Compare Psalms 19:7. It is called the law of liberty, or freedom because it is a law producing freedom from the servitude of sinful passions and lusts. Compare Psalms 119:45; Notes, Romans 6:16-18.
And continueth therein - He must not merely look at the law, or see what he is by comparing himself with its requirements, but he must yield steady obedience to it. See the notes at John 14:21.
This man shall be blessed in his deed - Margin, doing. The meaning is, that he shall be blessed in the very act of keeping the law. It will produce peace of conscience; it will impart happiness of a high order to his mind; it will exert a good influence over his whole soul. Psalms 19:11. “In keeping of them there is great reward.”