In the below verses we are given the Biblical command to examine ourselves, and prove whether we are in the faith of our Lord Jesus Christ - or not.
It is important to understand that by judging ourselves we do so, and can only do so, by the Holy Ghost. It is the spiritual man who can judge himself, and even all the world, because of the Holy Ghost given him by God, as well as his renunciation of and turning aside from the flesh - his carnal nature.
“Examine yourselves, whether ye be in the faith; prove your own selves. Know ye not your own selves, how that Jesus Christ is in you, except ye be reprobates?” - 2 Corinthians 13:5(also consider Galatians 6:4, and 2 Peter 1:10)
“For if we would judge ourselves, we should not be judged. But when we are judged, we are chastened of the Lord, that we should not be condemned with the world.” - 1 Corinthians 11:31-32 (also consider 1 Corinthians 11:28-34)
“But he that is spiritual judgeth all things, yet he himself is judged of no man.” - 1 Corinthians 2:15 (also consider 1 Corinthians 6:2-4).
An individual can only judge themselves (accurately) by the Holy Spirit’s presence within them. It is difficult for any man to examine themselves naturally speaking because of the prideful, sinful, nature of man. If we are to possess an accurate picture of ourselves, which is necessary to better serve God and to fulfill the biblical command of self examination; we must be filled with the Spirit, and cast aside our pride. This is why examining ourselves is so difficult, because if we are honest, we are miserable failures, which is not something anyone wants to admit. But this is what the Lord has told us from the beginning to the end of the scriptures. This is why our Lord Jesus came and paid the price; we cannot measure up to God’s high standard apart from Christ our righteousness (2 Peter 1:1, Romans 5:21).
Some Christians have a problem with the idea of Christians being failures. They somehow take this statement to be an attack on the righteousness of God's people and even an affront to the work which Christ does through believers. People who feel this way appear to be self-righteous and unattuned to the extreme perfection which the law demands. Perhaps they misunderstand the message which is meant to be communicated. Never there was a man who measured up by his actions only, only by his faith. Lest this be an argument of semantics, it should be stated clearly; Yes, Christians are more than conquerors through Him, our precious Lord and Savior Jesus Christ. But when we, as individual Christians measure ourselves against God and his perfection and supremacy, we cannot but help to see our insignificance and leanings toward a nature of sin. It is also true that we, per se, are not required to be measured against the standard of the law, for Christ cast that down in a sense (Romans 10:4). If we consider all the faithful patriarchs, none of them were perfect, even though they may have been described as righteous or faithful, and as prophets and men after God's own heart. Consider David and Abraham, they were men who were epitomies of faith and righteousness, and yet they failed at times (2 Samuel 11:1-27,Genesis 12:10-20, 20:1-18). And when we see the failures in their lives, and especially in our own (if we can see them, for many I fear cannot), we can point to these and consider ourselves miserable failures; though perhaps we are as perfect as a man can be by faith. When the accuser Satan points to our sins and says "see Lord, they are unworthy of your salvation," it is then that we can say "Lord we would be unworthy, but we have been made worthy by our faith in your Son." Then Christ our advocate will turn to the Father and say, "It is true, these are mine, for they had confessed these sins, my blood has covered them." (Ephesians 1:7, 1 John 2:1, Job 16:19, Revelation 12:10-11)
We cannot, it appears, move on to a more mature Christian walk, unless we are able to examine ourselves, see our sins, and confess them with the promise to be cleansed from them (1 John 1:9). This is also why spiritual men judge all and are judged by none; because it is not they that judge but God in them.
We should pray as Job did in Job 13:23 - “How many are mine iniquities and sins? make me to know my transgression and my sin.” We should pray as did David in Psalm 51:3 - “For I acknowledge my transgressions: and my sin is ever before me.” We must desire for the Lord to convict us so strongly of our sins, that we develop a hatred toward them and cannot but weep till we have departed from them.
Humble yourselves therefore under the mighty hand of God, that he may exalt you in due time: Casting all your care upon him; for he careth for you. Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour: Whom resist stedfast in the faith, knowing that the same afflictions are accomplished in your brethren that are in the world. But the God of all grace, who hath called us unto his eternal glory by Christ Jesus, after that ye have suffered a while, make you perfect, stablish, strengthen, settle you. To him be glory and dominion for ever and ever. Amen. - 1 Peter 5:6-11