Wayne Grudem offers several reasons why Jesus Christ must be fully human in order to save people from their sins in his excellent Systematic Theology. I offer a summary of five of these reasons below, along with Scriptural support.
- Representative Obedience. Jesus obeyed the commands of God where humanity failed to do so: “Therefore, as one trespass led to condemnation for all men, so one act of righteousness leads to justification and life for all men. For as by the one man’s disobedience the many were made sinners, so by the one man’s obedience the many will be made righteous” (Romans 5:18-19).
- Substitute Sacrifice. In order for Jesus’ death to be applied to humans, He had to become a human too: “Therefore he had to be made like his brothers in every respect, so that he might become a merciful and faithful high priest in the service of God, to make propitiation for the sins of the people” (Hebrews 2:17).
- Mediate Between God and Man. In taking on full humanity, Jesus is able to represent humanity to God and represent God to humanity: “For there is one God, and there is one mediator between God and men, the man Christ Jesus” (1 Timothy 2:5).
- Fulfill Man’s Purpose. God placed mankind on the earth to subdue and be God’s representative on the earth, but man fell into sin and failed to fulfill this purpose. Jesus Christ became a man in order to fulfill this purpose through His perfect obedience: “And he put all things under his feet and gave him as head over all things…” (Ephesians 1:22)
- Provide an Example. Jesus became human in order to demonstrate what true humanity looked like so that as man follows the example of Jesus, man becomes more fully human: “whoever says he abides in him ought to walk in the same way in which he walked” (1 John 2:6)
That in human nature he might on our behalf perfectly obey the whole law and suffer the punishment for human sin; and also that he might sympathize with our weaknesses.