Augustine is known for his statement: "Da quod iubes, et iube quod vis" which means "Give what you command, and command what you want." In this statement he was talking to God, surrendering himself completely to the will of God. Still, in this complete surrender he gave a condition: "give what you command." It is Augustine saying: "Ok Lord, you can command me to do anything that you want, BUT, there is a condition, you have to give me the ability and means to obey."
This phrase is what sparked the Pelagian controversy (Augustine recounts Pelagius getting angry when he heard it in "The Gift of Perseverence" 20.53).
We can ask with Pelagius: "How can a good God command something that we cannot do?" Augustine resoundingly responds: "Grace!"
Of course we cannot obey God's commands, that is why God gives us grace. We obey only by his strength which is a gift. All we are, all we say, all we do is a gift from our most gracious and loving creator.
God's love is so great that he knows we cannot live up to his standard, so he gives us what is needed to do so. All this so that we can be with him and enjoy him forever.
