This is not those two verses John 16:8-9 are saying.
The one who will convict the world is the Holy Spirit. The Holy Spirit convicts the heart of the born-again Christian as to their sin. If the born-again Christian listens to the Holy Spirit's conviction than usually that person will begin to change their behavior. That is one of the things that the Holy Spirit does, He leads us in righteousness through convicting us or showing us our sin.
You said:
Believing in Jesus is listening to his word and put it into practice,
The only people that the Holy Spirit judges and convicts are Christians. It is not a process of judging to say your wrong or your bad, it's a process of trying to sanctify us and make us more like our Father in heaven. That is a good process, that is not a negative judgement, but a positive teaching us.
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You said:
but if our decision is to continue living in our mistakes, discard salvation and our sins are still with us
This statement is not true. Our Salvation is a GIFT from Jesus. WE CANNOT take away our own Salvation. Our Salvation is not ours to take away. Our Salvation is Jesus Christ's. He decides. We cannot discard it or loose it. Jesus tells us that He will always forgive our sin.
1 John 1:9
" If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness."
Notice that it is HE who is faithful and HE who is just. It is not about us, it is about Jesus.
It DOES NOT say if we.... it says He.
Notice also that He purifies us from all unrighteousness. Again not us, but Him.
And, as you understand the next reading?
Matthew 25
The Final Judgment
31 “When the Son of Man comes in his glory, and all the angels with him, jthen he will sit on his glorious throne.
32 Before him kwill be gathered lall the nations, and he will separate people one from another as a shepherd separates the sheep from the goats.
33 And he will place the sheep on his right, but the goats on the left.
34 Then the King will say to those on his right, ‘Come, you who are blessed by my Father, inherit the kingdom prepared for you from the foundation of the world.
35 For I was hungry and you gave me food, I was thirsty and you gave me drink, I was a stranger and you welcomed me,
36 I was naked and you clothed me, I was sick and you visited me, I was in prison and you came to me.’
37 Then the righteous will answer him, saying, ‘Lord, when did we see you hungry and feed you, or thirsty and give you drink?
38 And when did we see you a stranger and welcome you, or naked and clothe you?
39 And when did we see you sick or in prison and visit you?’
40 And the King will answer them, ‘Truly, I say to you, as you did it to one of the least of these my brothers, you did it to me.’
41 “Then he will say to those on his left, Depart from me, you cursed, into the eternal fire prepared for the devil and his angels.
42 For I was hungry and you gave me no food, I was thirsty and you gave me no drink,
43 I was a stranger and you did not welcome me, naked and you did not clothe me, sick and in prison and you did not visit me.’
44 Then they also will answer, saying, ‘Lord, when did we see you hungry or thirsty or a stranger or naked or sick or in prison, and did not minister to you?’
45 Then he will answer them, saying, ‘Truly, I say to you, as you did not do it to one of the least of these, you did not do it to me.’
46 And these will go away into eternal punishment, but the righteous into leternal life.”