From Wayne Grudem’s Systematic Theology:
The definition of God’s knowledge given above also specifies that God knows “all things possible.” This is because there are some instances in Scripture where God gives information about events that might happen but that do not actually come to pass. For example, when David was fleeing from Saul he rescued the city of Keilah from the Philistines and then stayed for a time at Keilah. He decided to ask God whether Saul would come to Keilah to attack him and, if Saul came, whether the men of Keilah would surrender him into Saul’s hand. David said:
“Will Saul come down, as your servant has heard? O LORD, the God of Israel, I beseech you, tell your servant.” And the LORD said, “He will come down.” Then said David, “Will the men of Keilah surrender me and my men into the hand of Saul?” And the LORD said, “They will surrender you.” Then David and his men, who were about six hundred, arose and departed from Keilah, and they went wherever they could go. When Saul was told that David had escaped from Keilah, he gave up the expedition. (1 Sam. 23:11–13)
Wayne Grudem claims that God knows all things possible. If there is an option that I can choose to eat a ham sandwich or a turkey sandwich, God then knows each of those alternatives and the butterfly effect of those independent actions. For evidence, Grudem cites an instance in the life of King David where God tells King David what would happen if King David stayed in the city of Keilah.
Whether or not God knows “all possibilities” is besides the point. The evidence given is amazingly weak. If someone told me not to do something because something would then happen, my instant reaction would be to think that they hold additional present knowledge that I do not have. Assuming that they know “all possibilities” and all future chains of events would be a terrible leap of logic. It is not a rational conclusion.
The mere fact that in a systematic theology book this evidence is one of three evidences presented to defend “God knowing all possible futures” is reason to discount the statement as having serious Biblical evidence.
The other two evidences is Jesus insulting crowds saying that Tyre and Sodom would have repented with the evidence presented to his listeners. Even if this was not a biting hyperbole meant to insult the crowd, it still does not require infinite knowledge of all possibilities. Certainly God could survey those two cities to know their general demeanor.
When taking these texts against other texts that suggest some things never entered God’s mind, we should tread lightly on the over-inflating the scope of our evidence.