Was the 40-year wilderness part of God's plan, and does that mean God didn't make a valid offer to Israel?
Yes. The 40-year wilderness was part of the divine plan, yet God still made a valid offer to Israel. They could have entered the promised land at Kadesh Barnea, but God knew they would not; their failure did not negate His genuine offer.
Les explains that God’s eternal purpose and grace were given in Christ Jesus before the world began, not through the nation of Israel. Nevertheless, God made a valid offer to Israel—He was not playing games. At Kadesh Barnea they could have gone into the promised land of milk and honey. God told them to go in and take the land, promising to drive out the Canaanites with hornets, with the land ready and in production, and to drive them out slowly so weeds would not take over first. Israel did not do it, but the offer was still valid; they could have. God knew they would not, so the 40-year wilderness was in the divine plan, yet it was not because God failed to give them a valid offer.