Why must Christ's sacrifice be understood as a finished work?
Answered in 1 source
Christ's sacrifice is a finished work, which assures believers that all sin has been fully dealt with.
Understanding Christ's sacrifice as a finished work is foundational because it emphasizes the completeness of His atonement. The statement 'It is finished' encapsulates the idea that all necessary conditions for human redemption have been met. Hebrews 10:14 tells us, 'For by one offering He has perfected forever those who are being sanctified.' This means that believers are secure in their salvation, as it is not dependent on their works but entirely on Christ’s accomplished work on the cross. It frees believers from the burden of trying to earn or maintain their salvation through deeds, buoying their faith in the certainty of God's promises.
Commentary