Why is Christ's death at Calvary essential for salvation?

The significance of Christ's death lies in its role as a substitutionary atonement. According to 2 Corinthians 5:21, Christ was made sin for us, taking upon Himself the guilt and penalty due to His people. This act was necessary to fulfill the justice of God while also manifesting His mercy. By dying on the cross, Christ not only bore our sins but also imputed His righteousness to all who believe. Hence, His sacrifice is the means by which reconciliation to God is achieved and the eternal covenant of grace is fulfilled.