Do you know yourself?
David wanted this: knowing himself. And because he was a child of God, he especially wanted to know if there is sin in his life, that grieves God. Therefore he examined himself, his thoughts, his words, his ways he did things.
But in Psalm 139 David also shows that he is not putting too much trust in his own research. He is still afraid that there might be something left in his heart or in the rest of his life to his own attention has escaped.
Therefore he asks God to help him in this Psalm.
Namely, David believed that God knew him better than he knew himself.
It is important for us to research in our heart with God´s help. Sin is and remains an important factor in life, which children of God should consider seriously.
That is what Paul means when he writes: „Examine yourselves, to see whether you are in the faith. Test yourselves. Or do you not realize this about yourselves, that Jesus Christ is in you? - unless indeed you fail to meet the test! I hope you will find out that we have not failed the test.“ (2 Cor. 13,5-6)
Do you understand?