Hebrews 4:12 says that the word of God is living and effective. Perhaps that’s not so astonishing. For example, a scholar might say that the words of Shakespeare are living and effective, because they still have an impact on us today. People still go to Shakespeare plays and still read his works. People still marvel and take inspiration from Shakespeare’s words. In that sense, they are alive, and, in that sense, scripture, as God’s word, is alive as well.
But, Shakespeare’s words are not truly alive. Just because they affect people who are exposed to them, it doesn’t make them truly alive. The first time you see a dead body, maybe at a wake or in a morgue, the body produces a response in you. But, just because that body makes an impact on you, that doesn’t make it alive, except in a loose, metaphorical sense.
When commenting on Hebrews 4:12, St. Thomas Aquinas says that for something to be truly alive, it must have its own movement and activity. Neither Shakespeare’s works nor a dead body have their own motion or activity, and thus, they are technically dead. God’s word, on the other hand, is technically alive, “living and effective.” How so? In the beginning was the Word, and the Word was with God, and the Word was God. And the Word became flesh, and made his dwelling among us, and we saw his glory. That is why people pray over scripture, but not over Shakespeare: they find something in it that is truly living and effective: Jesus Christ.