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 Wis. 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.