Goodness, sorry, I didn't mean to kill a good post. Doesn't anyone here read French?
(me either.)
Try this:
1 Corinthians 15:24 Then cometh the end, when he shall have delivered up the kingdom to God, even the Father; when he shall have put down all rule and all authority and power.
25For he must reign, till he hath put all enemies under his feet.
26The last enemy that shall be destroyed is death.
27For he hath put all things under his feet. But when he saith all things are put under him, it is manifest that he is excepted, which did put all things under him.
28And when all things shall be subdued unto him, then shall the Son also himself be subject unto him that put all things under him, that God may be all in all.
Angels, being spirit only and eternal only, have a one time choice. The devils can't come back to God. Once they sinned, they were condemned eternally. But when God made man flesh, He made a way for man to sin and still come back. As long as man was alive in his flesh, he had unlimited choices of whether to do right or wrong. Knowing man would eventually make the wrong choice, He also had to make a way and a plan for Him to interact with man. That's why, Jesus is the lamb slain from the foundation of the world-not just since Adam's fall. Because God had already, with the temptation, made a way of escape.
That's also the reason that God drove Adam and Eve out of the garden. Not as punishment, not in cruelty, but to save them from themselves. If they had stayed and God hadn't guarded it, they would also have eaten from the tree of life. After they had sinned if they had eaten from the tree of life, they would have (just like the angels) been condemned forever.
These verses aren't discussing oneness or trinity. They are discussing a very different topic indeed-salvation. Since the foundation of the world, God's plan of salvation has been Jesus. When the end of the world has come, and final victory over death is won, we will no longer need a mediator in Jesus or salvation through him. At that point there will be no more need for the cross; our victory will be won.
Look in the end of Revelations. How often, as that prophecy progresses, is Jesus seen as a king, a victor, a ruler, a lion? How often is He seen as a lamb, as slain, and so forth? The focus at the end of time will change from our need of salvation to our victory in Christ.
Sorry if that doesn't make sense to all the deep theologians. Its hard to explain what I see without getting shot to pieces, because it isn't taught. But it seems to work, anyway.