12 For the word of God is living and powerful, and sharper than any two-edged sword, piercing even to the division of soul and spirit, and of joints and marrow, and is a Discerner of the thoughts and intents of the heart.
13 And there is no creature hidden from His sight, but all things are naked and open to the eyes of Him to whom we must give account.
God’s words are inseperable from God Himself (John 6:63)
living (v.12) — with the idea of constant activity
powerful (v.12) = engergizing
The words “the dividing asunder of soul and spirit,” do not mean “the dividing asunder from spirit.” Nor is it “the dividing asunder of joints from marrow.” It is a going through the soul, a going through the spirit. The dividing asunder here is not that of one thing from another, but of one thing in itself by the action of something separating its constituent elements from one another by piercing it. — Hebrews in the Greek New Testament, by Kenneth S. Wuest, page 89.
Discerner (v.12) = possessor of the power to judge.
thoughts (v.12) = ponderings, reflections
The idea (v.13) is that God knows our thoughts and motives and knows if we do or don’t believe.
naked (v.13) = to have the throat exposed. It is taken from the games, and signified to bend back the neck. Here the metaphor may be taken either from the sacrifice of a victim or from a mode of punishment. Whatever the metaphorical sense is, the warning is that there is no hiding oneself in any part of our being from God. — Hebrews, by W.E. Vine, page 270
So, the Jews needed to be sure to enter into the rest offered in Christ because a day is coming when they will be judged by the Word of God and God will know if they believe.
From a lesson I wrote:
What did the Hebrews think of when the writer used the word “sword”?
Chances are, they thought of the gladius, the Roman sword. It was much shorter than swords seen in movies, no more than two feet long. Soldiers didn’t swing them around either. They were primarily used for stabbing. A Roman soldier began a charge with a shield in his left hand and a pike or spear, in his right. He would dthrow his spear and then rush the enemy, grabbing his sword from his scabbard. He would attempt to knock his opponent’s weapon and shield up with the edge of his own shield, then stab with his sword. It wouldn’t be used defensively to deflect blows — that’s what the shielf was for.
The blade had a flattened-diamond cross-section with sharp edges down either side. When thrust forward by a muscular, trained soldier who was running toward his opponent, it could do a great deal of damage.