What if Jesus had failed? If he had died or fallen to temptation before completing his mission – he would have returned to the Father, “cap in hand”, saying, “Sorry Dad, I failed”. Leaving his earthly body behind.
Perfection also means completeness or fullness. Jesus had to “reach” the cross and be resurrected in his body. The journey he went on from birth to death, though he was born “perfect” he was still just “a perfect Spirit” in a mortal body.
Part of his journey was to “receive the Holy Spirit” (in the form of a dove). His life on earth involved the “perfection” of himself in perfect integration with his body. He and his, like us and ours, had to be trained into maturity. Before he was “ready” for the cross.
Though he never capitulated to temptation, he was, all the same, “contaminated” by his earthly body. He was just like us – his body produced desires, wants, and needs. Some of this is seen in his “typified” temptations, displaying bodily needs, eg food.
Also thoughts of world domination arose from “the mind of the flesh”. He refuted them all until he reached his goal – the cross. He was now ready to handle everything his fleshly body could throw at him – . Because he was now strong enough, in himself, his Spirit, to take on and utterly destroy sinful/human nature, within his own body.
And the Father watched his son endure the “agony of death”. He won “the battle” and it was “not possible for death to hold him”. The “prince of this world” (death) was dethroned. His body became immortalised. He was perfected within himself on the cross. He was “fully perfected” when he was resurrected.
We also travel this life as imperfect beings, in imperfect bodies. But we have imperfect spirits, as well as imperfect bodies, unless we are Christians, when we have HIS perfect Spirit within us, to also train and mature our abilities as we overcome.
If we die at any time, our spirit, which is “perfect” because of HIS Spirit, “returns to the Father”, or is captive to “sleep”, whichever way you want to look at it. Our bodies return to dust.
When we are resurrected, what we will be is yet to be revealed – there are varying glories of body – varying “rewards”. “With what kind of body will we come?” was the question – “but when we see him, we will be like him”.
If Jesus had died or failed “prematurely”, his perfect Spirit would have returned to God. As Christians, “premature death” simply means we are still perfect in him and so are saved. Unbelievers appear to be lost for eternity.
He was MADE READY for perfection – his perfection occurred ON THE CROSS, after which, that perfection was IMMORTALISED by his resurrection.