The Unpardonable Sin is simply to not believe the Gospel, its unpardonable because you cannot be pardoned unless you believe the Gospel: believe in Jesus Christ.
The Scripture is clear:
"I tell you the truth, all sin and blasphemy can be forgiven, but anyone who blasphemes the Holy Spirit will never be forgiven. This is a sin with eternal consequences.” He told them this because they were saying, “He’s possessed by an evil spirit.” (Mark 3:28-30).
The people committing the unpardonable sin and blasphemy against the Holy Spirit were rejecting Jesus as Savior, and saying He was doing things by the devil. No Christian can commit this sin.
The Scripture is clear:
"I tell you the truth, all sin and blasphemy can be forgiven, but anyone who blasphemes the Holy Spirit will never be forgiven. This is a sin with eternal consequences.” He told them this because they were saying, “He’s possessed by an evil spirit.” (Mark 3:28-30).
The people committing the unpardonable sin and blasphemy against the Holy Spirit were rejecting Jesus as Savior, and saying He was doing things by the devil. No Christian can commit this sin.
but Christians who revert to rejecting Christ commit the unpardonable sin of apostasy per Heb. 6:4-6.