How do we know 'It is finished' is true?

The declaration 'It is finished' is supported by numerous biblical affirmations that testify to the completion of Christ’s redemptive work. Hebrews 10:14 asserts that 'by one offering He has perfected forever those who are being sanctified,' confirming that Christ’s sacrifice was sufficient and did not need supplementary actions from humanity. Furthermore, passages like Daniel 9:24 highlight the prophetic assurance that God's plan through Christ would culminate in the full payment for sins. Thus, the truth of this declaration is rooted in scriptural testimony and the nature of God's promise to save His people entirely through Christ.