Hebrews 4:12 says: For the word of God is living and active. Sharper than any double-edged sword, it penetrates even to dividing soul and spirit, joints and marrow; it judges the thoughts and attitudes of the heart.
The emphasis in the passage is on the ability of God’s word to discern the heart behind the actions. Our human nature is subject to frailty and is a source of failure even when our heart is right. We are complex beings and often we, ourselves, don’t understand why we say or do or feel a certain way.
So what can I do about it? Shall I struggle with doubts and uncertainties? Shall I count on others to tell me what they think?
No, there is a rest for the people of God. Only he knows the difference between sin and rebellion on one hand and misunderstanding and human frailty on the other. All man can see is what is on the surface, and my own perspective is clouded. However, God has perfect vision and his word (not the Bible, but what he says) discerns to the most indiscernible parts of my life. If he speaks words of condemnation to me, it is because he sees rebellion in my heart. If he speaks words of comfort, it is because he sees my failure but also that I have failed with a pure heart.
You see, this passage isn’t intended to help us formulate some bilateral or trilateral view of human existence, it is to cause us to rest in the Lord and let him unravel our lives and our mysteries as to why we say, do, or feel as we do.