There is one sin that can NEVER BE FORGIVEN... even CHRIST stated that HE can do nothing for the person that commits that sin.
Matthew 12:31 32
31”Therefore I say to you, any sin and blasphemy shall be forgiven men, but blasphemy against the Spirit shall not be forgiven. 32”And whoever shall speak a word against the Son of Man, it shall be forgiven him; but whoever shall speak against the Holy Spirit, it shall not be forgiven him, either in this age, or in the age to come.”
The sin of blasphemy against the Holy Spirit - is - salvation itself. The work of Salvation is from the Holy Spirit, in that “man is dead” (spiritually dead, with the body catching up in a few decades, later).
Being that everyone is unable on his or her own to accept Jesus as their personal Savior (because of mankind’s sin nature, resident in him from birth) - the Holy Spirit intervenes to allow the person’s choice to be made, and also the Holy Spirit speaks directly to each person’s spirit in giving testimony to that person that God “is”, that He had made everything that one sees (of creation) and that God has provided a way of salvation, if they seek it out.
For the person to BLAPSHEME the Holy Spirit, is to say that the Holy Spirit is a LIAR and what the Holy Spirit is testifying to that person’s spirit is NOT TRUE.
THAT will not be forgiven, because that is rejection of the Saving work of God, through His Son Jesus.
IN OTHER WORDS - that person has rejected Salvation, and the rejection of Salvation IS THE ONE THING THAT WILL NOT BE FORGIVEN ... and will result in being cast into the lake of fire and being tormented forever and ever.