I’ll answer from a Pentecostal Protestant perspective (and much of what I say will apply to other evangelical Christians as well).
Judgment for the believer is three-fold. First, judgment occurs at the cross. At the cross, the believer pleads guilty, confesses his sin, and identifies himself with Jesus, his substitute. (John 12:31-32; 1 John 1:19). Second, there is ongoing self-judgment (1 Corinthians 11:31-32). Then finally, there is judgment before the judgment seat of Christ. For believers, this is not a judgment of condemnation, but one for determining the believer’s rewards (1 Corinthians 3:13-15).
We should always be examining our consciences. This is that second element in the self judgment of the believing Christian. As Paul says in 1 Corinthians 11:31-32, “But if we judged ourselves truly, we would not be judged. But when we are judged by the Lord, we are disciplined so that we may not be condemned along with the world.”
The Holy Spirit. This is part of His sanctifying work in the life of the believer.
We know we are separated from God mainly in two ways: 1) the agency of the Holy Spirit who brings conviction (i.e. He convinces us that we are sinners; John 16:18) and 2) the Word of God, which reveals to us the commands and oracles of God thereby showing us how far we have fallen short of God’s glory and righteousness.
When I have unconfessed sin in my life, I do feel separation from God. I feel burdened when I try to worship Him in church (no liberty), and I often feel uncomfortable having to sit through a sermon because the Word often touches on the theme of rebellion against God.
In addition, I often feel this tug of war within myself. Part of me wants to walk down to the altar and pray for forgiveness, while the other part of me wants to stay in the pew because that part of me is still unwilling to acknowledge my sin. But when I do go to the altar its as if I am laying down my sin and surrendering it to the Lord. When I get up, I know I’m leaving it there and not picking it back up.
I am having a living conversation with another person. His name is Jesus, and He’s more real than you or I. What is so wonderful about the Incarnation is that our God is not ignorant of what it is to be human. He was tempted and tried just as we are, yet He lived without sin. When I confess my sins to Him, He knows me so deeply and truly that He can understand my weaknesses and my faults. Neither does He despise my human frailties. I come to Him knowing that in Him is perfect love and righteousness.