4:12 word of God. Both the written Word (the Scriptures) and the living Word (the Lord Jesus Christ) would satisfy the statements in this verse, but the over-all context would indicate that the Scriptures are primarily in view (note Hebrews 4:2; also Hebrews 5:12-13; plus the fact that so many quotations from the Old Testament appear in Hebrews). The Scriptures indeed are “quick and powerful”—that is, “living and energizing,” able to impart to the reader both spiritual life and power (II Timothy 3:15-17).
4:12 two-edged sword. The “sword of the Spirit, which is the word of God” (Ephesians 6:17), is in reference to each individual “saying” of God, used as appropriate.
4:12 soul and spirit. There is a distinction between a person’s “soul” and his “spirit,” but they operate so much in concert that only the Scriptures can discern between them. The soul is probably the entity of conscious life and thought shared with animals, except that it is much more highly organized and complex in man, whereas the spirit is the entity that can be energized by the Holy Spirit, uniquely the “image of God” in man. Thus the soul and spirit seem to answer respectively to the “living and energizing” attributes of the Word. Note that man is indicated to be a tri-unity of “spirit and soul and body” in I Thessalonians 5:23, analogous in some respects to the divine Trinity. As far as the body is concerned, the sword of the Spirit can even divide between joints and marrow (again perhaps answering analogously to soul and spirit). The bone structure of the body is its skeletal framework; the “marrows” in these bones (the Greek is in the plural) constitute the engine that maintains the physical life of the body by producing its red blood corpuscles. In the original language, the relation between soul and spirit is illustrated by that between joints and marrow. That is, the sense can be taken as follows: “The sword of the Spirit pierces even to the dividing asunder of soul and spirit, even as a fine two-edged surgical knife in proper hands can separate the marrow from the bone joints containing it.”