In the beginning, God did not tell Adam and Eve they could not partake of the tree of life. When they listened to the lies of the evil one and lost not only their relationship with God, they also lost their opportunity to eat of the tree of life. This left man on his own, living from the tree of the knowledge of good and evil, and the result is sin as we see it in the world today. The root of all sin is pride. It has many faces, but the root is always the same. "I want to be recognized. I want to be independent." "I don't want to have to depend on God, because that would make me look weak." "I don't want anyone (including God) to tell me what to do." "I want to be esteemed for who I am on my own merits." For God to be able to take a man or woman into heaven for all eternity, this disposition must be dealt with. If God allowed one person into heaven with an independent, self-seeking spirit, heaven would cease to be heaven.
God never intended for man to live separate from Him. We were created to live in union with Him, finding fulfillment in that relationship. "For by Him all things were created that are in heaven and that are on earth, visible and invisible, whether thrones or dominions or principalities or powers. All things were created through Him and for Him. And He is before all things, and in Him all things consist" (Colossians 1:16-17). Man was created in the image of God with a capacity for choice and fellowship with God. But this fellowship can only be realized by the full provision of God: the Holy Spirit indwelling man and being the source of his life.
The world's condition, as we see it today in all its ugliness, is the result of men living separate from God. Although we may struggle to understand why, it had to be allowed. To deny men the choice to live separate from God would destroy the opportunity for true fellowship, because fellowship can only exist between those who desire and choose that relationship. Man's part is to freely give himself to God as a vessel through which the life of God can be revealed. God's part is to be the source of that life. The union of God and man is the glory of God's creation.
God was not taken by surprise by Adam's choice. He is Almighty God and He not only knew what would happen, but also what He would do about it. Calvary was not an afterthought--it was in the plan of God before the foundation of the world (1 Peter 1:20). Calvary was the way God chose to make a way for mankind to be righteous by partaking of His own life. In this way man can enter into true and lasting fellowship with God for all eternity. Since God always does things in perfection, we can conclude there was no other way for God to bring many sons to glory. The cross was God perfect answer to man's dilemma.