What did God give the human race so that they could respond to his love?
God gave the human race the indwelling attribute of will—a capacity to choose. This enables people either to respond to His love or to reject it. He also brought Satan on the scene so that this choice could be genuinely exercised, because angels could not respond in that way.
Les explains that God made the human race as objects of His love, and to be an object of love, the giver expects love in return. Angels could not respond, so God made the human race with the indwelling attribute of will to either respond to His love or reject it. Les also teaches that Satan was brought on the scene so that people could exercise that choice; otherwise there would be no will exercise. This connects with Ephesians 3:10 and the manifold wisdom of God according to His eternal purpose.