We must be free of sins to be divinely perfect or holy. Ezekiel 33:13, James 2:10.

If we are sure that we confessed our sins and they are remitted, we have become perfect (2 Corinthians 13:5). 

Remission of sins renders us perfect until we sin again. When we sin again and ask for forgiveness and do not sin, we regain our perfection. Jesus is always ready to forgive us freely. Thus, if we do not confess our sins and overcome them, we cannot be saved (1 John 1:9).

We can recognize that we reach perfection if we compare all our behavior with the will of God in Moses and the Prophets (Luke 16:29-31) and can conclude that we are behaving exactly according to the will of God, without any disagreement in behaviour and belief.

It does not matter that anyone thinks that we are of the devil because they do not know or understand the correct will of God in Moses and the Prophets. What matters is that we inspect our system of belief (faith, trust) against the will of God (Luke 16:29-31) and we do not find any contradiction with it (2 Corinthians 13:5, James 2:10) in order to live to its fullest the kingdom of God which is within us (Luke 17:20-21), His people (John 10:14, 15, 27, Revelation 18:4), to be ready to see His face in His brand-new (not restored) world to come because our heavens and earth will disappear being burned out (Revelation chapter 21, Isaiah 65:17; 66:22; 2 Peter 3:13).

1 John 1:8-10 ASV

(8)  If we say that we have no sin, we deceive ourselves, and the truth is not in us.
(9)  If we confess our sins, he is faithful and righteous to forgive us our sins, and to cleanse us from all unrighteousness.
(10)  If we say that we have not sinned, we make him a liar, and his word is not in us.

Luke 24:47 ASV
(47) and that repentance and remission of sins should be preached in his name unto all the nations, beginning from Jerusalem.

2 Corinthians 13:5 ASV
(5)  Try your own selves, whether ye are in the faith; prove your own selves. Or know ye not as to your own selves, that Jesus Christ is in you? unless indeed ye be reprobate.

1 John 2:1-2 ASV
(1)  My little children, these things write I unto you that ye may not sin. And if any man sin, we have an Advocate with the Father, Jesus Christ the righteous:
(2)  and he is the propitiation for our sins; and not for ours only, but also for the whole world.

True. Jesus died for all sinners BUT His sacrifice is only useful for the repentant sinners who take advantage of it.

Because God does not listen to sinners (John 9:31) and the Holy Spirit does not intercede on behalf of any sinner (Romans 8:27)!

Jesus came to bring all sinners to repentance (Luke 5:32) not to meet the sinners in their sins without repenting or changing their behavior to be conformed with the will of God in Moses (Romans 12:2).

Once we repent and, as such, Jesus forgives our sins, we become a new holy (saint) creature without sin with the expectation to not ever sin according to Ezekiel 33:13, James 2:10, and Isaiah 1:2-20.