Why did Christ come to save us all when he did? Why didn't he come when Adam and
Eve sinned in the Garden of Eden? Why didn't he save us then?
Your Question is in line with similar ones I have heard in that 'Why didn't God just deal with the sin of Adam and Eve right then and there? Why did He let things go on? The direct answer to this goes with the truth that we do not and can not know why God does what He does and why He chooses any specific time. His timing is always correct;
But when the set time had fully come, God sent his Son, born of a woman, born under the law, 5 to redeem those under the law, that we might receive adoption to sonship. Gal. 4:4-5
Also at the time of Adam and Eve's sin, God proclaimed man as fallen. He had to punish
them for the sin right then. Since man was now fallen, he was separated from God
from that point. This is why God, as an act of grace allowed them to live, but no
longer in the midst of the Garden. Man would, from this point have to prove his dedication
to God. God knew man's way back to Him would only be through salvation. By an act
of Grace from Him..... Jesus, our Lord and Savior. Scripture show us this in the
book of Genesis when God spoke to the serpent
"And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise they head and thou shalt bruise thy heel." Gen. 3:15
The 'bruising of the heal' is in reference to the crucifixion of Jesus. God knew, although Satan caused man to sin, Man was His creation and that in the end He would prevail.
Why did God send Jesus? Read the scriptures and see how many accounts of people sinning against God. How many times God showed his mercy? All He commanded was for man to love and worship Him. Personally, I think God sent Jesus, became God in the flesh to once more be in direct contact with Him as it was in the beginning. This was a fulfillment of scripture. The Old Testament speaks about the coming Messiah which did in fact happen. For Him to make the sacrifice. Man committed the sin that caused the fall, man had to pay price. So in His Mercy, He "sent His only begotten son so that all who should believe in him shall not perish but have eternal life" (John 3:16)
It certainly makes sense to me that Jesus would have come when He did. Man needed to learn the Laws of God. To learn what God had expected of him. To learn by example from God Himself. If Jesus had come right at the onset, God knew man would have distant himself more and more from Him and His word as we are today, then what? Send someone else? As the scriptures say, It was His plan, when the time was right (fullness of time), to set things straight;
"But when the fullness of time was come, God sent forth His Son, made of a woman, made under the Law." Gal. 4:4