Much of the core of the new is derived from prophecy found in the old. How the prophecy is 'encouraged' to fit is open to a lot of debate and speculation but with the aid of generous shoehorn it has been achieved. The story of the birth in Bethlehem is a great example of a size ten foot fitting into a size seven shoe.
The new is in the old contained
The old is in the new explained
........or something like that.