All Sins of All People for All Time Have Already Been Forgiven
You are Already Forgiven: The sins of all people for all time have been forgiven because Jesus Christ died for you. Forgiveness happened on the Cross of Christ, not after like many teach. The Bible clearly says that without the shedding of blood there can be no forgiveness (Hebrews 9:22). You are forgiven, but new and eternal life comes only when you trust Jesus Christ as your Savior.
2 Corinthians 5:19 namely, that God was in Christ reconciling the world to Himself, not counting their trespasses against them, and He has committed to us the word of reconciliation.
Hebrews 8:12 For I will be merciful to their iniquities, and I will remember their sins no more.
Hebrews 10:18 Now where there is forgiveness of these things (sins), there is no longer any offering for sin.
Colossians 1:20 and through Him to reconcile all things to Himself, having made peace through the blood of His cross; through Him, I say, whether things on earth or things in heaven.
Mark 3:28 "Truly I say to you, all sins shall be forgiven the sons of men, and whatever blasphemies they utter;
Hebrews 10:12 but He, having offered one sacrifice for sins for all time, sat down at the right hand of God. (Meaning the forgiveness was finished.)
Romans 5:10a For if while we were enemies, we were reconciled to God through the death of His Son, ... (Notice this verse says we were reconciled while we were enemies, not after we become friends with God.)
Colossians 2:13 When you were dead in your transgressions and the uncircumcision of your flesh, He made you alive together with Him, having forgiven us all our transgressions, (Again, forgiveness happened before we became believers in Jesus Christ.)
Romans 6:10 For the death that He died, He died to sin once for all; but the life that He lives, He lives to God.
Hebrews 2:9b ... Jesus, because of the suffering of death crowned with glory and honor, that by the grace of God He might taste death for everyone.
Hebrews 9:26b ... but now once at the consummation of the ages He (Jesus) has been manifested to put away sin by the sacrifice of Himself.
John 1:29 The next day he (John the Baptist) saw Jesus coming to him and said, "Behold, the Lamb of God who takes away the sin of the world!"
1 John 2:2 and He Himself is the propitiation for our sins; and not for ours only, but also for those of the whole world.
The Unforgivable Sin: The Sin of Unbelief
The Holy Spirits convicts the world of its unbelief. Since eternal life is found only in Jesus Christ, rejecting Jesus is the same thing as rejecting His eternal life. Also, and very important, the Holy Spirit does not convict you of your individual sins since God has already forgiven and forgotten all your sins (Hebrews 8:12). It is your own conscience, other people or religious systems that cause feelings of guilt and remorse.
John 16:8-9a "And He (Holy Spirit), when He comes, will convict the world concerning sin, and righteousness, and judgment;  concerning sin, because they do not believe in Me; ...
Mark 3:29 but whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin.
Luke 12:10 "And everyone who speaks a word against the Son of Man, it will be forgiven him; but he who blasphemes against the Holy Spirit, it will not be forgiven him.