Repentance is a vital part of a Christian's life. There's no part of our life that isn't tainted by sin. Even every one of our prayers has a hint of sin to it. If not for God's justification, every one of our prayers would still be filthy rags.
Before Christ, we chose to openly rebel against Him. There was nothing in our lives that could be pleasing. The noetic effects of our sin means that our mind is fallen, and naturally we cannot understand the things of God (1 Cor. 2:14).
Because the carnal mind is enmity against God: for it is not subject to the law of God, neither indeed can be. So then they that are in the flesh cannot please God.
Romans 8:7-8
The Holy Spirit convicted us of our sin, and we turned from our old ways towards Jesus. Without Him, our life would still be filled with malice towards Him and others (Titus 3:3-7). The Spirit justifies us, in that, He is the one doing the work. We feel His will and power to do God's will (Phil. 2:13). We experience new desires, and a new outlook on life and God- a new thing is made (2 Cor. 5:16-17).
Yet we live in this doctrinal reality of the "already, but not yet." The Church is currently Christ's Bride, but the wedding happens in heaven. There are promises we only see partial fulfillment of in this life, just glimpses of what is to come for us (1 Cor. 13:12). We are new, but that doesn't mean that our newness is complete. But we have what is essential for our present reality.
So we still have indwelling sin (1 John 1:8). We are still tempted. The Spirit is constantly at war with our sin, and His desires are contrary to our natural ones (Gal. 5:17). Contrary to a popular phrase, that every Christian just will sin, John the Apostle says that he's reminding us of things that should keep us from sin if we are faithful (1 John 2:1). That those in Christ do not keep on sinning (1 John 3:6). Though we're not fully born again, those who live in Christ don't sin (1 John 3:9).
Without the justification by grace through faith in Christ, all our actions are sinful (Rom. 14:23). We have to choose the Spirit's desires (Gal. 5:16).
Though this is not a yin-yang dichotomy, where evil is plainly evident. We don't always know when a sin is committed. It could be that we do a good thing, but our inward desire was evil. We can be so ignorant of what's good and evil. We must have a good definition of sin, and be open to the work of the Spirit. We must be suspicious of our own actions and beg Him to cleanse us from secret faults (Psalm 19:12-14).
Not all objects of sinful desires are sinful. All sin starts by twisting the truth to our desire- removing God's glory from it (Rom. 1:21-32). We can sin in the base desire we have or to the degree that we want something. A lust is when we sin to get something, or sin when we don't get something. Sometimes, our desires are good, but we overstep by wanting them too much in going after them in a sinful way. It starts with inward desire. No one makes us sin. Then, when we commit to the lust's line of thinking, it gives birth to sin. And sin brings forth death (James 1:13-15).
All sin is equal. God's perfect authority is behind every command, and by transgressing one command we're effectively breaking all of them (James 2:10-11). We can sin by actively committing a transgression against God's standard. Or sin by omitting following God's standard. This can be on purpose, or in ignorance. Yet even in ignorance, God holds us to His standard (Lev. 4:27-28).
Jesus is God's perfect standard. He lived a sinless life. He suffered, and didn't lash out or complain (1 Peter 2:23). He loved and rebuked out of His love. He followed His Father's commands and abode in His love (John 15:10). He gave us a command to keep, that we love God and one another (John 15:12-14).
In this command, we see all God's commands fulfilled (Rom. 13:8-10). One may think that to defeat sin, we have to focus on not doing it. But instead we see that focusing on Jesus Christ is the victory. The joyful expectation of seeing His face drives us to submit to His purification, even as He is pure (1 John 3:2-3). He has achieved His victory over sin and over the works of the Devil (1 John 3:8). He took away the sting of death in sin. He welcomes us to walk with Him in His victory over sin (1 Cor. 15:54-57).
So then we joyfully follow His commands. They aren't grievous- our faith that sprung from Him overcomes the world (1 John 5:3-4). We follow His command to repent, and turn towards Him.
He's forgiven us. Which means that our sins won't be "remembered" in the Day of Judgement (Jer. 31:33-34). Positionally, we're right with Him. But relationally on a day-to-day basis, we have sins that are at odds with Him, which makes it necessary to still repent.
We grieve the ways we have wronged Him inwardly and outwardly. We grieve that we've hurt His heart. There is such a thing as godly sorrow- godly shame and guilt. Shame is sorrow for who we are. Guilt is sorrow for what we've done. Worldly shame and guilt emphasize our own ideals of what we should be or should be doing. Godly sorrow puts the emphasis on how we don't put God's ideals first and therefore fall short of His glory. We experience death in worldly sorrow, but God gives life in godly sorrow (2 Cor. 7:9-11).
This is demonstrated in several places in Scripture, and it is summed up in Jesus' command that we deny ourselves and follow Him (Luke 9:23). Job hated himself (based on God's rebuke,) repented in dust and ashes, and turned towards God. God accepted Job's repentance (Job 42:2-7). God said to Israel that He would punish them, yet would bless and accept them. They would look on their ways, hate themselves, and would know the Lord who'd done them good for their disobedience (Ezek. 20:40-44).
The first step is confession. Yet, this is not the same as repentance. Confession is admitting to God and/or others that we have wronged them. Repentance is actually then walking in the relationship with and holiness of the Lord. We're getting ourselves out of the way so that we can see the Lord more plainly.
Job confessed that he was evil (Job 40:4). Yet, God rebukes him for the next two chapters to get him to repent- to deny himself and follow the Lord. We should not stop short of repentance, but be full of faith that He is faithful and just to forgive us of our sins, and to cleanse us of all unrighteousness (1 John 1:9). This means confessing and being sorrowful to an attempted full extent of our sin, each time. The thought of sackcloth and ashes makes most Christians in "sophisticated society" uncomfortable. But when we bring ourselves strategically low, God lifts us up (James 4:9-10).
Worldly sorrow does not take comfort in the promises of God or accept forgiveness, it only feels bad for not living up to selfish expectations. Like Judas' suicide (Matt. 27:3-5). Repentance does not include abusing one's body, speaking unbiblical standards to oneself, or continuing to ask forgiveness for a sin- as if Christ was a liar and wasn't sufficient to atone. This "works death," and as opposed to godly sorrow, this sort of repentance must be repented of (2 Cor. 7:10).
There are some considerations. Shame and guilt are not strictly feelings, they are things that exist before the judgement seat of God. Therefore, do no wait to feel like repenting, but do it with the understanding of God's just cause and that He will supply the heart necessary to repent if we ask. Although sinful motives may be present in prayer, and in many of our actions, there isn't always a sin committed. There may not be need for feelings of guilt, because while sinful motives are always present, they are not always obeyed. We still deny ourselves in this case so that we don't settle for lesser sanctification, and ask God to give us better desires. Mistakes do not need to be repented over. The sins of others do not need to be repented over- they are not ours, and we will not be condemned for them (Deut. 24:16). However, if we are acting in line with the sins of others, God may treat us as He did them (Deut. 5:9).
Since we're not yet fully perfected, this process of confessing and repenting will repeat throughout the Christian life. Walking in humility for us means that we live with a heart open to the idea that every one of our actions could have sin buried in it, hidden just beneath the surface. And that by following His command to repent, our conscience will be cleared (2 Cor. 7:11). We become blameless- not that we couldn't be blamed for any sin. But that we blame ourselves first- no one feels the need to voice our sinful faults because we're voicing them and taking steps necessary to remove those sins. Like Paul (1 Tim. 1:15-16).
There is a need to remove things that hinder us from honoring and enjoying God. Flee when they appear (1 Thess. 5:22). Put those things in you to shame (Col. 3:5-10). Disarm and dismantle the false thoughts by speaking God's true Word to yourself (2 Cor. 10:4-5). Cut them off (Matt. 18:7-9). Make every effort to put off specific sins and put on good works and thoughts, or else one idol will be exchanged for another. A Christian who is filled with hope and courage to face sin is one who takes always the next biblical step, seeing that God is faithful to keep moving them along.
Put off the old man, and put on the new man, who's being created in righteousness and true holiness. Put off lying and speak truth with your neighbor. Put off ungodly anger, not giving the Devil a foothold, and put on God's anger designed to move you towards a clear goal. Put off theft and put on honest work towards giving to one who is in need. Put off corrupt communication, but only speak words that would edify. Do not grieve God's Spirit. Put off all twisted, selfish intentions and put on Christ's kind intentions towards even those who wronged Him (Eph. 4:22-32).
Jesus suffered being tempted, and is able to help those who are tempted (Heb. 2:18). He knows what it's like to be tempted in every way just like we are. He intercedes for us and we can come to Him with confidence that He will welcome us and provide sufficient grace and mercy (Heb. 4:15-16). He loves a broken and contrite heart- He will not turn us away in it. Alongside such an attitude, believe that nothing that we do can provide a perfect sacrifice or make it up to God (Psalm 51:16-17). Jesus did that. Now, go and attempt to sin no more in this life (John 8:10-11).
For in my holy mountain, in the mountain of the height of Israel, says the Lord God, there shall all the house of Israel, all of them in the land, serve me: there will I accept them, and there will I require your offerings, and the firstfruits of your oblations, with all your holy things.
I will accept you with your sweet savour, when I bring you out from the people, and gather you out of the countries in which you have been scattered; and I will be sanctified in you before the heathen.
And you shall know that I am the Lord, when I shall bring you into the land of Israel, into the country for which I lifted up my hand to give it to your fathers.
And there shall you remember your ways, and all your doings, in which you have been defiled; and you shall hate yourselves in your own sight for all your evils that you have committed.
And you shall know that I am the Lord, when I have wrought with you for my name's sake, not according to your wicked ways, nor according to your corrupt doings, O you house of Israel, says the Lord God.
Ezekiel 20:40-44