Hebrews 10:26 - Matthew Poole's English Annotations on the Holy Bible

If we sin wilfully: the severe exaction which God will take upon such as apostatize from him, is further enforcing the former duty, and is introduced by the particle for, to that end; if we by a free and spontaneous desertion of Christ, and his ordinances, without a coercion by threats and persecutions; and this after we had professedly in our judgments, wills, and affections, with faith and reverence, acknowledged a love and subjection to the true gospel doctrine of the way of bringing sinners to God by Christ our great High Priest, 1 Thessalonians 8:31, 1 Thessalonians 14:6, which was made known to them by Christ and his apostles, and confirmed by miracles and the gifts of the Holy Ghost, so as to profess a full conviction of this truth, so as to assent and consent to it. After that we have received the knowledge of the truth; after all this, to renounce the profession of it, and to forsake the assemblies where it is held forth; this is the spontaneous and wilful sinning: see Hebrews 6:6. There remaineth no more sacrifice for sins: this is unpardonable by the just constitution of God in the gospel, because no sacrifice can atone God for them, without which they cannot be pardoned; and the sacrifice of Christ, which only could do it, they renounce and desert; and so this, nor any other they can bring, can procure pardon for them, so that their sins remain in guilt and power on them, and between them and God's wrath are they like irrecoverably to be ground to perdition.