Jesus was truly God and truly human. If Jesus were not truly God, he could not save us and forgive us. (Heresies such as Arianism and Ebionitism were rejected by the early church because they did not recognize Jesus as fully God.) If Jesus were not fully human, he could not be the authoritative example for faithful living. (Heresies such as Docetism, Gnosticism, Apollinarianism, Monophysitism, and Marcionism were rejected by the early church because they did not recognize Jesus as fully human.) As fully human and fully God, Jesus can fully relate to our struggle and has the power to fully save us.   

Scripture - John 1:14