How do we know that Christ's death was substitutionary?

Christ's death is fundamentally substitutionary because He took upon Himself the sins of humanity, satisfying divine justice. The concept of substitution involves someone taking the penalty due for another. As stated in Romans 5:6-8, while we were still sinners, Christ died for us, demonstrating His role as our substitute. His sacrifice was predetermined in God's counsel, as Peter affirms in Acts 2:23, indicating that even the choices of wicked men served God's redemptive purpose. The entire Old Testament sacrificial system points to Christ’s ultimate sacrifice on the cross, further validating His role as the substitute for sinners and the fulfillment of God's plan for salvation.