How do we know Jesus' work on the cross is sufficient for salvation?

We know Jesus' work on the cross is sufficient for salvation because He proclaimed, 'It is finished' (John 19:30), indicating that His sacrifice fully satisfied the just requirements of God. According to Hebrews 9:26, He appeared once at the end of the age to put away sin by the sacrifice of Himself, signifying that His atonement was not just possible but guaranteed for His elect. Furthermore, His resurrection and ascension to the right hand of the Father reaffirm His victory over sin and death, showing that His work is not ongoing but complete and accepted by God (Romans 8:33-34).