1. Why is confession important in a Believer's life? What is sin?

When I kept silent about my sin, my bones wasted away
Through my groaning all day long.
For day and night Your hand was heavy upon me;
My vitality was drained away as with the heat of summer. Selah.
I acknowledged my sin to You,
And my iniquity I did not cover up;
I said, “I will confess my transgressions to Yahweh;"
And You forgave the iniquity of my sin. Selah. (Ps 32:3-5, LSB)

But you, why do you judge your brother? Or you again, why do you view your brother with contempt? For we will all stand before the judgment seat of God. For it is written,
“As I live, says the Lord, to Me every knee shall bow,
And every tongue shall confess to God."
So then each one of us will give an account of himself to God. (Rom 14:10-12, LSB)

2. How does God view a Believer's confession? How does Jesus view a Believer's confession?

If they confess their iniquity and the iniquity of their fathers, in their unfaithfulness which they committed against Me, and also how they walked in hostility against Me - I also was walking in hostility against them, to bring them into the land of their enemies - or if their uncircumcised heart becomes humbled so that they then make up for their iniquity, then I will remember My covenant with Jacob, and I will remember also My covenant with Isaac and My covenant with Abraham as well, and I will remember the land. (Lev 26:40-42, LSB)

And do not fear those who kill the body but cannot kill the soul. Rather fear him who can destroy both soul and body in hell. Are not two sparrows sold for a penny? And not one of them will fall to the ground apart from your Father. But even the hairs of your head are all numbered. Fear not, therefore; you are of more value than many sparrows. So everyone who acknowledges me before men, I also will acknowledge before my Father who is in heaven, but whoever denies me before men, I also will deny before my Father who is in heaven. (Matt 10:28-33, ESV)