God can guess better than anyone else, perhaps. But in order for you to have true free will, your decisions must remain unknown until you make them. If all your future actions are already written in stone, free will is only an illusion. At best, God can know all of your possible choices and the choice that you are most likely to make. But there always has to be a margin of error for free will to truly exist.
When you look in the eyes of grace, when you meet grace, when you embrace grace, when you see the nail prints in grace’s hands and the fire in his eyes, when you feel his relentless love for you - it will not motivate you to sin. It will motivate you to righteousness.