26 For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins, 27 but a certain fearful expectation of judgment, and fiery indignation which will devour the adversaries. (Hebrews 10:26–27, NKJV)
Those who believe a Christian can never fall from grace and be lost (as Galatians 5:4 says can happen) falter and fall over this passage. The “once saved, always saved” doctrine refuses to believe and accept its clear warning against willful sin. The “we” of verse 26 are Christians who sin willfully. The sin being discussed happens “after we have received the knowledge of the truth” (a figure of speech for one’s salvation by the gospel, 1 Timothy 2:4; 2 Timothy 2:25). When Christians sin willfully (voluntarily) they should not think they will have another path of redemption. That is flawed thinking. There will not be another sacrifice given for their sins. Christians who sin intentionally can expect a sure judgment of God’s fervent wrath. “The Lord will judge His people” who willfully turn away from Christ (Hebrews 10:30). The impossibility of apostasy (Calvinism’s “perseverance of the saints”) denies the Bible by denying the outcome of a Christian’s willful sin. The issue is not about God’s power to save (the “sacrifice for sins” has been fully made). The issue is about Christians choosing to reject Christ to practice sin. For them, judgment is certain, fiery and full (Hebrews 10:31). So, exercise your faith and do not sin willfully.