Hebrews 4:12 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.
Most conservative Christians understand the "word of God" as referring to a thing--usually the Bible. But this explanation does not make sense when the verse is taken in context.
Hebrews 4:12-13 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. 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.
Some would argue that the Bible is simply being personified but I think this misses the point. The "Word of God" is not a what but a who. Although most commentators since John Calvin understand the "word of God" as referring to either the Bible or the message of the Gospel, most patristic commentators understood the "Word of God" as referring to the Divine Logos--Jesus Christ Himself.
There are many churches that seem to exalt the Bible above God. This is just as foolish as exalting your own reason above God's Word. The Word of God first and foremost is Jesus. Jesus is able to discern are thoughts and intentions because He is God. The Scriptures are the word of God in a secondary sense because they are all about Jesus. Many seem to believe in Jesus because He is understood as one of the many things that Scripture tells us about but this is entirely backwards. We believe the Scriptures because they tell us about Jesus and have been given to us by the Triune God.
The Bible is like an infallible icon of Jesus. If I had a photo of my wife and I started showing it around and talking about the photo paper that was used and the background but never said anything about my wife I you might learn quite a bit about how the picture was made but you would never really learn anything about the main subject of the photo. All you would have is a bunch of mildly interesting facts. The same is true of Scripture. If someone can preach a sermon on a passage of Scripture without Jesus as the main subject then the person is not preaching the Scriptures. Those who hear such sermons on a regular basis are really not much worse off than if they sat under a pastor who completely denied the authority of the Scriptures.