Christ suffering was not just as a living sacrifice but a glimpse and exercise of all suffering God was cognizant that we all undergo, showing that Christians also must carry their cross or their own problems and burdens to death at times so to speak. Jesus needed to be fully man and sinless to be the way, truth and the life. If he werent sinless he would be baseless. The holy spirit was the gift that he gave to his followers which was the bridge from death to life.

He is the aggregate or image of our transformed being in heaven, showing the nature of endpoint of saved creation, where we are sinless and prevail over sin. the Spirit of his message needed to communicate that he was the Alpha and Omega of time itself and therefore he is always the same throughout birth death and resurrection.

Also, Jesus did not die in sin because Satan is the origin and cause of all sin, if Jesus were otherwise he is not God in human form and wouldn't be able to triumph Satan for all mankind. Satan needed to be deceived that God in human form could be overpowered. Satan most likely didn't know half the story of Christs plan, only bits through Messianic prophecy and by observable prophecies.