Hebrews, Chapter 4, begins with the Sabbath rest. Paul was explaining why sabbath rest is crucial.
Therefore a sabbath rest still remains for the people of God. And whoever enters into God's rest, rest from his own works as God did from his. Therefore, let us strive to enter in to that rest, so that no one may fail after the same example of disobedience.
Indeed, the word of God is living and effective, sharper than any two-edge sword, penetrating even between soul and spirit, joints and marrow, and able to discern reflections and thoughts of he heart.
No creature is concealed from him, but everything is naked and exposed to the eyes of him to whom we must render an account.
In Biblical times, words were regarded as powerful--to the point once a word is spoken it becomes an independent thing. The word of God is powerful. It goes forth and it does things. Those words are effective and do what they are designed to do. They are for all time. For example, would anyone argue the benefits of a day of rest?
Also, before God, there are no pretenses, no cons. He sees our very thoughts, and our intents. He sees the truth of us.