Why can God plan for every contingency without taking away free will?
God can plan for every contingency because, before creation, the Godhead foreknew exactly what every person and nation would do. That foreknowledge lets Him sovereignly prepare for all outcomes without coercing choices; people and nations still exercise genuine free will to accept or reject Him.
Les explains that this is one aspect of God's sovereignty that is hard to comprehend: God is in control of everything, yet He never takes away the free will of men and nations. Before He ever created anything, the Godhead could look down through the eons of time and knew exactly what every person in every nation would do. That is called foreknowledge. With foreknowledge, He could also plan for any contingency because He knew what was going to happen, and yet He never took away the free will of mankind. Israel had absolute freedom to accept Him and have the kingdom, but they also had the free will to reject it. Their rejection did not throw God a curve, because He knows what they are going to do.