In st Johns apocalypse, it talks about taking the mark will be an unforgivable sin. In the gospels , we learn that there are no unforgivable sins apart from blasphemy ( rejecting God) Then why would taking a mark be suddenly unforgivable ?
because it is a way of accepting the antichrist who is a blasphemer, just as Baptism is a way of professing faith in Christ as the Son of God, our Lord and only Saviour.