How do we know that Jesus' death was accomplished?

In Luke's account of the transfiguration, it is stated that Moses and Elijah spoke with Jesus about His 'decease' which He would accomplish at Jerusalem (Luke 9:31). The use of the term 'accomplished' indicates that His death was not a loss but a completion of His mission. This accomplishment signifies the fulfillment of all Old Testament prophecies and sacrificial systems, as He is the ultimate Lamb who takes away the sins of the world. As highlighted in Hebrews, Christ's sacrifice once for all is sufficient for the atonement of God's elect, assuring believers that their sins have been fully dealt with and that they stand justified before God. Thus, Jesus' death is indeed accomplished, marking the victory of grace over sin and death.