From Bruce A. Ware. God’s Lesser Glory: The Diminished God of Open Theism:
Consider especially the force of the concluding statement in verse 21. God says, “I know their intent which they are developing today, before I have brought them into the land which I swore.” God knows their future rebellion, for he specifically predicts it with certainty and in some detail before it occurs. Furthermore, this passage helpfully illustrates a point made earlier: that God can know something fully in advance and yet express the appropriate emotion and ethical response to that situation when it actually arises in its historical unfolding. Knowing something in advance does not preclude real relational interaction. action. God knows fully what Israel will do and he enters fully into intimate mate relationship with them, hot with emotion and deeply involved in response to the wickedness of their sin.
This is a quote in a book written against Open Theism, leading a reader to believe Ware would be using prooftexts meant to convince Open Theists of the errors of their ways. Deuteronomy 31:21 is a particularly bad verse to use as exhaustive knowledge of all future events. Pretend the phrase “I know their intent which they are developing today” was absent (notice also how Ware crops the word “for/because” from the start of the quote). Any Open Theist would predictably answer the charges that not only can God know the future because He knows people’s general tendencies, but God also has direct and current knowledge of Israel’s present state. The interesting thing is that this is exactly how this section is worded. God predicts a lot of things in the future and then claims He knows that future because of His present knowledge (“for I know their intent which they are developing today”). Ware’s prooftext is evidence of Open Theism.