What does the Bible say about the eternal security of the believer?

The concept of eternal security is rooted in Scripture, particularly in Psalm 125, which asserts that those who trust in the Lord are like Mount Zion, immovable and abiding forever. This image signifies the steadfastness of God’s people, emphasizing that nothing can separate them from His love or remove them from His grace. The perfection of Christ's sacrifice is fundamental to this doctrine. Because Christ’s death was effectual and fully satisfied the justice of God, those whom He died for will never perish. Thus, the security of the saints hinges not on their faithfulness, but on the faithfulness and perfection of Christ’s work on their behalf.