"Quick" or living, and "powerful" or efficacious, are regarded by many as meaning nearly the same thing; but "living" designates what is valid, what continues in force, as opposed to what is dead and no longer existing; and "efficacious" refers to the effect, capable of producing the effect designed. Exclusion from rest as to unbelievers was still living, still in force, abiding the same without any change. See 1 Peter 1:23, 25. It was also in full power so as effectually to exclude from rest all who did not believe. And then to prevent every evasion, so that no one might think a mere profession sufficient, or rather to guard against the incipient seduction of sin, he compares this "word" to a sword which can dissect the whole wellcompacted frame of man, so that even the very marrow may be discovered; and then passing from this simile, he says that this "word" is capable of judging the thoughts and purposes of the heart. And in order to identify as it were this "word" with God himself; he immediately refers to God's omniscience. The design of the Apostle seems to have been to guard the Hebrews against the deceitfulness of sin; so that they might not give heed to any of its hidden suggestions.
Stuart makes the transition from the "word" to God at the end of the twelfth verse, and renders the clause thus, "He also judgeth the thoughts and purposes of the heart." But this clause may more properly be viewed as explanatory of what is said of the two-edged sword.