How do we know the doctrine of unpardonable sin is true?

The truth of the unpardonable sin is established through various scriptural references, most notably in Matthew 12:30-32 and Hebrews 10:26-29. In Matthew, Jesus articulates a clear warning about the blasphemy against the Holy Spirit, which is seen as a fundamental rejection of divine truth. Hebrews 10 elaborates on this by indicating that willfully sinning after receiving the knowledge of the truth leaves no further sacrifice for sins. This teaches us that rejecting the singular atonement of Christ after acknowledging its truth results in dire consequences, as it denies the only means of salvation. Thus, the completeness of apostasy in relation to the work of the Holy Spirit affirms this doctrine through a careful examination of Scripture.