Why do Christians believe that Jesus had to be both God and man?

For Jesus to be an effective Savior, He had to be both fully God and fully man. As God, He possesses divine authority and ability to bear the weight of sin; as man, He represents humanity and bears the penalty for sin on our behalf. Hebrews 4:15 underscores this necessity, noting that He was tempted in every way as we are, yet without sin. This dual nature made Him the perfect mediator, enabling Him to fulfill God's requirements for justice while also extending grace and mercy to us. The significance of this truth is emphasized throughout the New Testament, highlighting that only through the God-man could genuine reconciliation between God and mankind be achieved.