God has one way that He allows humans to judge themselves and others. By the Holy Spirit, each of us is able to discern good and evil, choosing the good. We can and do know. The Holy Spirit is able to bring us to repentance (a new mind). The battle is for the mind. This is how anyone can be born again. This is the process by which each born-again person can overcome the sinful nature–by the Holy Spirit. When dealing with others, the Holy Spirit may lead us to deliver each other from sin through comfort, building up in Christ, teaching, admonition, or encouragement (exhortation). This form of judgement, whether concerning self or others, is for deliverance from the sinful human nature.
The fallen human nature loves to judge others. It even likes to condemn itself sometimes. This is because the self is sold into sin. (Romans 7:14) Satan is the king of the fleshly nature. He is the accuser. The fleshly nature loves to accuse. It loves to compare and cause divisions. (2 Corinthians 10:12)
However, we have been bought with the price of the blood of Jesus Christ. If we will receive it, we are not only pardoned, but Christ is imparted to us. (Romans 8:10, Romans 8:18, 2 Corinthians 4:6-7, Galatians 1:15-16, Galatians 2:20, Galatians 4:19, Ephesians 3:17, Colossians 1:27, 2 Thessalonians 1:10, 1 Thessalonians 2:13, 1 John 4:2-3, 2 John 1:7) We all have a fallen human nature. There is no one who isn’t tempted, drawn away by his or her own fleshly desires. (James 1:14) The fallen human nature can’t be reformed. It can’t do any righteousness at all. Any self-generated righteousness is as filthy rags. The Christ in us cannot do any sin. He is holy and incapable of sin. (1 John 3:9)
When we judge each other or our own selves in a fleshly way, we are judging Christ in us. We are failing to discern the Body of Christ. In the process of walking with Christ, He is being formed in us. This is a process of building up. King James Version calls it “edification.” From here forward, we are to know ourselves and each other after the spirit and not after the fleshly nature. (2 Corinthians 5:16)