Once believed, the response is two-fold: the individual recognizes that he is living a life of sin, and, perhaps for the first time, it repulses him! He wants to be forgiven, and to be given a fresh, clean start; that is called repentance. At the same time, because he believes that Jesus died for his sins, he responds with gratitude and love for his Savior. It is a two-sided coin. That is why Jesus told His disciples to preach repentance AND remission of sins (Lk. 24:47)! Repentance is man's response when he believes what Jesus did for him on the cross, and remission describes what Jesus did on the cross!
Jesus said, "For this is My blood of the New Testament, which is shed for many for the remission of sins" (Mt. 26:28). And the writer of the Book of Hebrews, explained the price Jesus paid for our remission: "And almost all things are by the law purged with blood; and without shedding of blood is no remission" (Heb. 9:22). The reason he said "almost," is because there is one sin that a man can commit, that is not covered in the shed blood of Christ: the blasphemy of the Holy Ghost. Jesus said, "But if I cast out devils by the Spirit of God, then the kingdom of God is come unto you. Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men" (Mt. 12:28, 31).
The Holy Spirit provided the evidence that was necessary for the Pharisees to believe in Jesus; when they rejected it, in so doing, they rejected Him; they were, for all practical purposes, calling the Holy Spirit a liar! They refused to repent and accept Jesus as their Lord. Therefore, they died in their sins (Jn. 8:24)!
Only the sin of denying Jesus is unforgivable.