Footnote
Ellicott's Commentary for English Readers
(12) As in Hebrews 3:12 the warning against the "evil heart of unbelief" is solemnly enforced by the mention of the "Living God," so here, in pointing to the peril of disobedience, it is to the living power of the word of God that the writer makes appeal. But in what sense? Does he bring before us again the word of Scripture, or the divine Word Himself? Outside the writings of St. John there is no passage in the New Testament in which the word of God is as clearly invested with personal attributes as here. The word is "quick" (that is, living), "powerful" (or, active--mighty in operation, as most of our versions render the word), "able to discern the thoughts of the heart." Philo, whose writings are pervaded by the doctrine of the divine Word (see the Note appended to St. John's Gospel in Vol. I. of this Commentary, p. 553), in certain passages makes use of expressions so remarkably resembling some that are before us in this verse that we cannot suppose the coincidence accidental. Thus, in an allegorical explanation of Genesis 15:10, he speaks of the sacred and divine Word as cutting through all things, dividing all perceptible objects, and penetrating even to those called indivisible, separating the different parts of the soul. But though these and the many other resemblances that are adduced may prove the writer's familiarity with the Alexandrian philosophy, they are wholly insufficient to show an adoption of Philo's doctrinal system (if system it could be called) in regard to the divine Word, or to rule the interpretation of the single passage in this Epistle in which an allusion to that system could be traced. Nor is the first-mentioned argument conclusive. There certainly is personification here, and in part the language used would, if it stood alone, even suggest the presence of a divine Person; but it is not easy to believe that in the New Testament the words "sharper than a two-edged sword" would be directly applied to the Son of God. In this Epistle, moreover (and even in this context, Hebrews 4:2), reference is repeatedly made to the word of God in revelation, without a trace of any other meaning. The key to the language of this verse, so far as it is exceptional, is found in that characteristic of the Epistle to which reference has been already made--the habitual thought of Scripture as a direct divine utterance. The transition from such a conception to those of this verse was very easy; and we need not feel surprise if with expressions which are naturally applied to the utterance are joined others which lead the thought to God as Speaker. It is, therefore, the whole word of God that is brought before us--mainly the word of threatening and judgment, but also (comp. Hebrews 4:2 and the last member of this verse) the word of promise.
Piercing even to the dividing asunder . . .--Rather, and piercing even to the dividing of soul and spirit, both joints and marrow. For the comparison of God's word to a sword see Isaiah 49:2; Ephesians 6:17; (Revelation 1:16); comp. also Wisdom Of Solomon 18:15-16, "Thine Almighty word leapt down from heaven out of Thy royal throne . . . and brought Thine unfeigned commandment as a sharp sword, and standing up filled all things with death." The keen two-edged sword penetrates even to dividing soul and spirit (not soul from spirit), with unfailing stroke severing bone from bone and piercing the very marrow. The latter words, by a very natural metaphor, are transferred from the material frame to the soul and spirit.
And is a discerner . . .--Is quick to discern, able to judge, the thoughts (reflections, conceptions, intents) of the heart. Man's word may be lifeless, without power to discriminate, to adapt itself to a changed state or varying circumstances, to enforce itself: the Spirit of God is never absent from His word.
Gill's Exposition of the Entire Bible
For the word of God is quick and powerful,.... This is to be understood of Christ, the essential Word of God; for the Word of God was a known name of the Messiah among the Jews; See Gill on John 1:1 and therefore the apostle makes use of it when writing to them: and the words are introduced as a reason why care should be taken, that men fall not off from the Gospel, because Christ, the author, sum, and substance of it, is the living God, omnipotent and omniscient; for not a thing, but a person is spoken of, who is a Judge, and a critical discerner of the secrets of men's hearts: and certain it is, that this Word is spoken of as a person, and is said to be a priest in the following verses; to which may be added, that the several things said of the Word exactly agree with Christ: he is "the Word of God"; as the word is the birth of the mind, he is the only begotten of the Father; he is the Word that spoke for the elect in the council and covenant of grace, and that spoke all things out of nothing in creation; he is the Word that has been promised, and spoken of by the prophets from the beginning of the world; and is the interpreter of his Father's mind, and our Advocate with the Father: he is
quick, or, as it may be better rendered, "living"; he has life in himself as God, he is the living God; he is the living Redeemer and Mediator, and he lives for ever as man; he is the author and giver of life, natural, spiritual, and eternal: and he is powerful, as he appears to be in the creation and sustaining of all things; in his miracles and ministrations; in the work of man's redemption; in the preservation of his people, and in his advocacy and intercession:
and sharper than any twoedged sword; or "more cutting than one", by the words of his mouth, by the power of his Spirit, and the efficacy of his grace; for his mouth itself is as a sharp sword, and out of it comes forth one, Isaiah 49:2 by which he pierces the hearts of men, cuts them to the quick, and lays them open. Jehovah is called a twoedged sword with the Jews (m); and Philo the Jew speaks of the flaming sword of the Logos
.
Piercing even to the dividing asunder soul and spirit, and of the joints and marrow; the like property Philo the Jew ascribes to the "Logos", or Word; he calls him "a cutter", and says he cuts and divides all things, even all sensible things, yea, atoms, and things indivisible (o); the apostle seems here to have respect to the several names with which the soul of man is called by the Jews, , "soul, spirit, and breath" (p); the latter of these, they say, dwells between the other two. Some by the soul understand the natural and unregenerate part in man, and by the spirit the renewed and regenerate part, which though sometimes are not so easily distinguished by men, yet they are by Christ; others think the soul designs the inferior faculties, the affections; and the spirit the superior ones, the mind and understanding; but the apostle's meaning seems to be this, that whereas the soul and spirit are invisible, and the joints and marrow are covered and hid; so sharp and quick sighted, and so penetrating is the divine Word, that it reaches the most secret and hidden things of men: and this sense is confirmed by what follows,
and is a discerner of the thoughts and intents of the heart; Christ knows what is in man; he is the searcher of the hearts, and the trier of the reins of the children of men; and this will be more apparent at the last day, when he will make manifest the counsels of the heart, and will critically inquire, and accurately judge of them.