In the great minds of the "founding fathers"
Gods plan took a detour because of freakin Adam and Eve and so plan B had to be put into motion since there was no such thing as a " remake human" or " Start over" project on the table.
Since JESUS spent a zillion years with his father the time came for them to temporary depart ways...what happens when someone you dearly love - your own child--has to leave home for the next 33 years- even though you know in advance for the sake of saving the lives of strangers!!