How do we know Christ's atonement is effective for salvation?

The effectiveness of Christ's atonement for salvation is assured by its nature and purpose. It is explicitly shown that His sacrifice was designed to be sufficient, achieving what the Old Testament sacrifices could not. Hebrews 10:14 tells us that by one offering, Christ has perfected forever those who are sanctified. This underscores the complete and final nature of His sacrifice, which not only covers sin but also purifies the conscience of believers (Hebrews 9:14). The outcome of His atonement is that it grants access to God, as stated in Hebrews 10:19-20, allowing believers to enter the holy presence of God with confidence, assured of their acceptance through Christ.