Zacharius Ursinus, the primary author of the Heidelberg Catechism, wrote a helpful explanation of the sin against the Holy Spirit (Mt. 12:31). The title of one part of this section is called “Certain Rules to be observed in relation to the Sin against the Holy Ghost.” Here they are:
1. The sin against the Holy Ghost is not found in every wicked person; but only in those who have been enlightened by the Holy Ghost, and who have been fully convinced of the truth, as Saul, Judas, etc.
2. Every sin which is against the Holy Ghost is reigning sin, and a sin against conscience, but not the reverse [e.g. sin that does not reign in a person and sin that is not against the conscience – spl]. For it may occur that some one may, either ignorantly, or even knowingly and willingly, hold certain errors, or violate some of the commandments of God, from weakness, or torture, or from fear of danger, and yet not purposely and maliciously impugn the truth, or totally fall from holiness, and continue in sensuality and a contempt of all that is sacred; but he may return unto God and repent of his sin. These forms of sin differ, therefore, as genus and species.
3. The sin against the Holy Ghost is not committed by the elect, or those who are truly converted. They can never perish; for Christ safely preserves and saves them. “They shall never perish, neither shall any man pluck them out of my hands. (John 10:28. Also, 2 Tim. 2:19. 1 Pet. 1:5. 1 John 5:15.) Hence those who sin against the Holy Ghost were never truly converted and called. They went out from us, because they were not of us.
4. No one should decide hastily or rashly concerning the sin against the Holy Ghost; yea, judgment should in no case be passed upon any one, unless it be a posteriori, for the reason that we do not know what is in the heart of man.
Covenant Presbyterian Church, OPC
Hammond, WI, 54015