His main argument was that God knows everything that we will do and therefore we don’t have true agency. (A very common argument, meant to place the blame for our lives on God and not ourselves.)
My rebuttal is this. God is omniscient, he does know everything. But,we don’t. We have no knowledge in this mortal state of what our individual future will hold. We have only the knowledge of the present moment and the past here on earth. Thus our agency is in absolute full force.
We can decide for ourselves, “I will make it to live with God again, no matter what.” If we act appropriately, following the guidelines prescribed by God to make it to the Celestial Kingdom, there is nothing that says, “oh, sorry, you’re slated for the Telestial Kingdom, too bad!”
Therefore, my ignorance of God’s knowledge of my future makes me innocent enough to believe that I can have all that He’s promised me. I have the choice and the ability here and now, to make that come to pass. Or I can decide I don’t want it. That’s my choice. My lack of knowledge makes it so.