We believe that God’s will happens no matter what. We also know we have free will to do what we please. Somehow our free will never gets in the way of God’s will. It is a great mystery.
Many times people unknowingly do God’s will through their own free will. For example, when you are having a really bad day, you haven’t told anyone about it, but they mysteriously say or do something that comforts you. That was God comforting, but He performed his will through one of His children through their own will. If you ask that person, they won’t say God told them to do it. They will say they just thought it would be nice. God didn’t force them to do it. It was their own free choice, and yet it fulfilled God’s will.
Much like the stories in the Bible, I believe God sometimes does choose a person for a specific purpose. However, in His perfection, he can somehow have other people around to fill in if the chosen person through their free will goes in a different direction. God is patient. He could make His will happen instantly, but He doesn’t need to.
“prepared for you” to me is speaking to God’s followers as a group. The only thing we need is love, so the kingdom we inherit is love. We won’t have need for food or water or anything else. Even if it is speaking to each person individually, God knows the future. He knows the list of everyone that will be in heaven at the end, so of course, He can prepare for each individual person if He wants to. Just because he knows how the story ends doesn’t mean he is meddling with it.