If Jesus were a man who could not have failed in his mission, there would be no way for us to relate to him. His life would become devoid of meaning because we relate to others based on our experience. Our experience tells us we can fail. If Jesus were God he could not have failed, and therefore could not be somebody with whom we can relate. The doctrine of the double nature of Christ strips us of a true appreciation of the challenges he faced and the manner in which he handled them.
Consider the account of Satan's attempt at tempting Jesus in the wilderness. (Mt. 4:1-11)
If Jesus really were God...
1.) Satan would not have even bothered tempting the One who could not have failed.
2.) Jesus would not have constantly been referring to God as a separate person and how Jesus should not put Him to the test.
3.) It would have been pointless for Satan to offer "all the kingdoms of the world" to Jesus since it is only by God's allowance that Satan has control over them.
4.) Satan's request for Jesus to worship him would have been absurd to both of them.
5.) Jesus would never have said, "Begone, Satan! for it is written, 'You shall worship the Lord (Jehovah) your God and him only shall you serve.'" (Mt. 4:8-10) RSV. Jesus said that his worship belongs to God, not Satan. If Jesus was God, this statement would make absolutely no sense at all.
Jesus always spoken of as a single being
We find no passage in the Bible in which it is taught that Jesus had two natures, one human and one divine...but he is always spoken of as a single being, "the Christ the Son of the Living God." Jesus constantly spoke of himself using the personal pronouns, "I", "myself", and "me". His Father (the One Jesus described as "the only true God"; John 17:1-3) is also overwhelming identified in the Bible by the singular person pronouns "I," and "Me," and "He," and "Him". That is because God and His son Jesus do not have dual or tri-natures. Jesus, being in God's image (2 Cor. 4:4) was only one...just as God is only one. (Deut. 6:4; 1 Tim. 2:5)
The Bible says that Christ AND Man (Col. 1:15; 2 Cor. 4:4) are in God's image. If it is true that God possesses a tri-nature, then why does Man (who was created in God's image) not display any kind of a multi-nature about him whatsoever? Certainly if God and Christ possessed such dual or tri-natures, and such a fundamental multi-nature aspect is conspicuously absent in Man, how then could it be said that Man was made in God's image?
"For there is one God, and one mediator between God and men, a man, Christ Jesus." (1 Timothy 2:5) (God Himself has no tri-nature and there was no dual nature for Jesus.)
Jesus' death
The argument that only the human part of Jesus died is a denial that God died for us. So the doctrine of the double nature of Christ not only conflicts with Scripture, it conflicts with other trinitarian dogma:
A comparable difficulty faces Trinitarians when they assert that only the human part of Jesus died. If Jesus were God, and God is immortal, Jesus could not have died. We wonder how it is possible to maintain that 'Jesus' does not represent the whole person. Nothing in the Bible suggests that Jesus is the name of his human nature only. If Jesus is the whole person and Jesus died, he cannot be immortal Deity. It appears that Trinitarians argue that only Deity is sufficient to provide the necessary atonement. But if the divine nature did not die, how on the Trinitarian theory is the atonement secured?
"Are you not from of old, O Lord my God, my Holy One? You shall not die." *
(Hab. 1:12) NRSV. (If Jesus were God, and God is immortal, Jesus could not have died.)
"Jesus, whom God raised from the dead, and we all are witnesses of this." (Acts 2:32) NLT. (If Jesus were God, did Jesus then raise himself up from the dead?)
God's Law to ancient Israel required "soul for soul [or, life for life]." (Exodus 21:23) So the death covering mankind's transgressions would have to equal what Adam had lost. Only the death of another perfect man could pay the wages of sin. 1 Timothy 2:6 & Romans 5:16, 17 outline that Jesus was such a man. Jesus was "a corresponding ransom" for the saving of all redeemable mankind descended from Adam.
For more, see:
Dual Nature of Christ (JWQ&A)
Is Jesus God?
Trinity Indexes
Examining Trinity 'Proof Texts'