I have heard many people claim that they are sinless but have never seen it. One would only need to accompany them throughout the day to discover how sinful they really are.

To make this claim shows they are prideful and self deceived; which does not make them sinless but sinful. Why; because Jesus said that we still have sin, even as believers. The people who claim this cannot see they are in sin, they are spiritually blind. Therefore they are

There fringe groups, cults and individuals who believe they have achieved this are removed from reality. The idea that we can be perfect- exactly like Jesus BEFORE a bodily transformation described in Rom.8, 1 Cor. 15 goes against the Bible and cannot be supported by any of the apostles teachings.

Are these people actually saying they are always faithful, in all things? The Bible says anything that is not done in faith is sin. Sin interferes with our fellowship, our relationship with God and men. We can go on thinking nothing has changed but from God’s perspective it has. God looks at the inner man, the heart for faith, which will lead to obedience, sin will always interfere with our faith. This is why we need to deal with it as soon as possible to have a clear conscience.

After healing a blind man Jesus said, "For judgment I have come into this world, that those who do not see may see, and that those who see may be made blind." Then some of the Pharisees who were with Him heard these words, and said to Him, "Are we blind also?" Jesus said to them, "If you were blind, you would have no sin; but now you say, 'We see.' Therefore your sin remains.”(John 9:39-41). It is often the most religious of people that do not see themselves as having any sin and are called blind by Jesus.

Paul makes this statement Rom 6:6-7 knowing this, that our old man was crucified with Him, that the body of sin might be done away with, that we should no longer be slaves of sin. For he who has died has been freed from sin.

At first this sounds like he is saying we have become sinless, however if read in context he goes on to say V.11-13 “Likewise you also, reckon yourselves to be dead indeed to sin, but alive to God in Christ Jesus our Lord. Therefore do not let sin reign in your mortal body, that you should obey it in its lusts. And do not present your members as instruments of unrighteousness to sin, but present yourselves to God as being alive from the dead, and your members as instruments of righteousness to God.”

Rom.6:6 done away Gr. katargeo- to render idle, unemployed, inactivate, or inoperative --to deprive of force, influence, or power. That so we should no longer be in bondage to sin…and the present active infinitive of douleuoo (NT:1382), continue serving sin (as slaves). (from Robertson's Word Pictures in the New Testament)

The phrase mortal body should not be overlooked, it is key. Paul qualified this statement by saying mortal body. Because an immortal body has already dealt with the presence of sin that would bring death to the body.

Paul is saying we are to have control (by the Holy Spirit) to resist, strive against sin. One does not resist something that is no longer a reality, that can affect them.

Rom 6:12 Reign basileuetoo (NT:928). Present active imperative, "let not sin continue to reign" as it did once (Rom. 5:12).(from Robertson's Word Pictures in the New Testament)

Rom 6:13 “ Stop presenting your members or do not have the habit of doing so, "do not go on putting your members to sin as weapons of unrighteousness."(from Robertson's Word Pictures in the New Testament)

To be sinless means one is perfect, they have reached the end of their sanctification. If your not a sinner then you are saying that you have no guilt or shame when you sin (yes you do sin.)

Do they who  think of themselves as perfect see others are perfect or only them.

Or is this a form of Narcism (Concern only for oneself: self-centeredness, egoism, self-absorption, self-importance, self-love. An immodestly high opinion of one's own worth.) Because one cannot claim they as a Christian are sinless (perfect) without having this same opinion of others.

But doesn’t the Bible say we are now perfect?

Heb 6:1 “Therefore, leaving the discussion of the elementary principles of Christ, let us go on to perfection, not laying again the foundation of repentance from dead works and of faith toward God” This word means maturity in doctrine not perfect, as in being sinless. Besides look at the adjectives - to go on to means we have not achieved this yet.

2 Cor 13:9 “We are glad whenever we are weak but you are strong; and our prayer is for your perfection (NIV). The NIV fails to communicate what is really being stated.

2 Cor 13:7-9 “Now I pray to God that you do no evil, not that we should appear approved, but that you should do what is honorable, though we may seem disqualified. For we can do nothing against the truth, but for the truth. For we are glad when we are weak and you are strong. And this also we pray, that you may be made complete.”

complete- Greek- katartisis- a strengthening, a perfecting of the soul, a training, disciplining, instructing from 2675; thorough equipment (subjectively): (Strong's Concordance).

Would one need to pray for the saints to do what is honorable  if one being complete in Christ means to be perfect?

James 3:2 “For we all stumble in many things. If anyone does not stumble in word, he is a perfect man, able also to bridle the whole body.”

Greek- telios which means to bring to an end, there is nothing more to complete, in both moral and mental areas.

Know anyone who does not make a mistake in their speaking?

Eph 4:12-14: “for the equipping of the saints for the work of ministry, for the edifying of the body of Christ, till we all come to the unity of the faith and of the knowledge of the Son of God, to a perfect man, to the measure of the stature of the fullness of Christ; that we should no longer be children, tossed to and fro and carried about with every wind of doctrine, by the trickery of men, in the cunning craftiness of deceitful plotting”

Here again we have the concept of the collective event, the whole church being brought to the fullness, which is by the resurrection. Notice he speaks of being influenced by error and the trickery of men, something a perfect sinless person would not be susceptible to.

For now 2 Cor. 5:1 ‘For we know that if our earthly house, this tent, is destroyed, we have a building from God, a house not made with hands, eternal in the heavens. In the future the completion of our redemption.”

Why is it destroyed? Because we still have sin in it. Jesus saw death an enemy. Paul said death will be the last enemy that would be defeated not the first (1 Cor.15:21,26,54-56). This is why Paul would not despair because Christ had come, 2 Cor 1:9: ‘Yes, we had the sentence of death in ourselves, that we should not trust in ourselves but in God who raises the dead.’

This is why Paul speaks of a future transformation of the body that has sin. First we gain control in the mind which gives us self control over our sinful body in our daily life. Rom 12:2: “And do not be conformed to this world, but be transformed by the renewing of your mind”

Eph 4:22-23:“that you put off, concerning your former conduct, the old man which grows corrupt according to the deceitful lusts, and be renewed in the spirit of your mind”

 Col .9-10 “Do not lie to one another, since you have put off the old man with his deeds, and have put on the new man who is renewed in knowledge according to the image of Him who created him”

Rom 8:13:  “For if you live according to the flesh you will die; but if by the Spirit you put to death the deeds of the body, you will live.”

Col 3:5 “Therefore put to death your members which are on the earth: fornication, uncleanness, passion, evil desire, and covetousness, which is idolatry.”
 Paul tells us to do this because sin is still present in the world and with us. We are to overcome it as much as possible.

Christ works His grace to us while we live as sinners.

Rom 5:8 “God demonstrates His own love toward us, in that while we were still sinners, Christ died for us.”

Gal .2:17 "But if, while we seek to be justified by Christ, we ourselves also are found sinners, is Christ therefore a minister of sin? Certainly not!”

Paul says even our being justified we still are sinners. He explains that sin dwells in us. “But now, it is no longer I who do it, but sin that dwells in me. For I know that in me (that is, in my flesh) nothing good dwells; for to will is present with me, but how to perform what is good I do not find.” (Rom 7:17-18).

Rom 7:24-25:  “O wretched man that I am! Who will deliver me from this body of death? I thank God-- through Jesus Christ our Lord! So then, with the mind I myself serve the law of God, but with the flesh the law of sin.”

So we have an internal war of being righteous with our mind but unrighteous with the body. 2 Cor 1:9 “Yes, we had the sentence of death in ourselves, that we should not trust in ourselves but in God who raises the dead,

Paul explains the event of Rom.8 is necessary, this great transformation that the whole world waits for to be set back into order.

1 Cor. 15:50-55 “Now this I say, brethren, that flesh and blood cannot inherit the kingdom of God; nor does corruption inherit incorruption. Behold, I tell you a mystery: We shall not all sleep, but we shall all be changed-- in a moment, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised incorruptible, and we shall be changed. For this corruptible must put on incorruption, and this mortal must put on immortality. So when this corruptible has put on incorruption, and this mortal has put on immortality, then shall be brought to pass the saying that is written: "Death is swallowed up in victory." "O Death, where is your sting? O Hades, where is your victory?"

This is a event that the whole church experiences together, not as individuals. and it is the LAST enemy to be dealt with (1 Cor.15:26).

V.56-57 The sting of death is sin, and the strength of sin is the law. But thanks be to God, who gives us the victory through our Lord Jesus Christ.

In other words if we die, it proves the presence of sin is with the body.  But if this were a one time event then Paul not tell us to cooperate in the power of the spirit. It is by the resurrection that the sin presence is dealt with and not until then.

Rom 8:18-23 “For I consider that the sufferings of this present time are not worthy to be compared with the glory which shall be revealed in us. For the earnest expectation of the creation eagerly waits for the revealing of the sons of God. For the creation was subjected to futility, not willingly, but because of Him who subjected it in hope; because the creation itself also will be delivered from the bondage of corruption into the glorious liberty of the children of God. For we know that the whole creation groans and labors with birth pangs together until now. Not only that, but we also who have the firstfruits of the Spirit, even we ourselves groan within ourselves, eagerly waiting for the adoption, the redemption of our body.”

If you are sinless then you will not die, you won’t need a resurrection if you are already sinless (perfect). There would be no need for the body to be redeemed, transformed from corruptible to incorruptible if we already achieved sinless perfection. Notice Paul says we have the firstfruits of the spirit and wait for the body. It is up to the Lord when this day will occur that will transform us from having sin to being sinless. And nobody you or I know, no believer has achieved this.