Hebrews 4:12

For--Such diligent striving (Heb 4:11) is incumbent on us FOR we have to do with a God whose "word" whereby we shall be judged, is heart-searching, and whose eyes are all-seeing (Heb 4:13). The qualities here attributed to the word of God, and the whole context, show that it is regarded in its JUDICIAL power, whereby it doomed the disobedient Israelites to exclusion from Canaan, and shall exclude unbelieving so-called Christians from the heavenly rest. The written Word of God is not the prominent thought here, though the passage is often quoted as if it were. Still the word of God (the same as that preached, Heb 4:2), used here in the broadest sense, but with special reference to its judicial power, INCLUDES the Word of God, the sword of the Spirit with double edge, one edge for convicting and converting some (Heb 4:2), and the other for condemning and destroying the unbelieving (Heb 4:14). Rev 19:15 similarly represents the Word's judicial power as a sharp sword going out of Christ's mouth to smite the nations. The same word which is saving to the faithful (Heb 4:2) is destroying to the disobedient (Co2 2:15-16). The personal Word, to whom some refer the passage, is not here meant: for He is not the sword, but has the sword. Thus reference to Joshua appropriately follows in Heb 4:8. quick--Greek, "living"; having living power, as "the rod of the mouth and the breath of the lips" of "the living God.

— Jamieson-Fausset-Brown Commentary (public domain)