Actually Screwtape, OT does mention you should love God, not just obey. It's the First Commandment I believe. Thou shalt love The Lord your God with all your heart, mind, and soul. Get it right so your argument can't be falsely debated.
That's not how commandment goes at all. It's "Thou shalt have no other gods before me" (Exodus 20) or if we go with the Exodus 34 version, it's "For thou shalt worship no other god: for the Lord, whose name is Jealous, is a jealous God". Either way, nothing about love, but plenty about obeying.