Why Would God Command Something That Is Impossible?

1. God clearly does command us to do that which is impossible for fallen sinners: "Be ye therefore perfect, even as your Father which is in heaven is perfect" (Matthew 5:48). Moreover, the law of God itself demands to be obeyed perfectly, flawlessly (James 2:10)—thus demanding a level of obedience that has proven utterly impossible for every person who ever lived, except Christ.
   
2. Therefore the fact that God commands us to do something is no proof that we have intrinsic power in our fallen state to obey Him. (Cf. Romans 7:15-16).
   
3. One major reason God gives us moral standards we cannot obey is to reinforce our knowledge of our own spiritual impotence, so that we have no option but to turn to His grace as we seek salvation from our sin. (Cf. Luke 18:13-14).
   
4. Nothing but sheer arrogance and a blindness to one's own spiritual poverty would lead anyone to think he is capable of obeying God or saving himself through human will power. (cf. Luke 18:11; Romans 10:3.)
   
5. It is also a serious mistake to imagine that inability nullifies responsibility in the moral realm. The fact that sinners are spiritually dead and therefore morally unable to obey God does not remove them from the moral obligation to obey Him.
   
6. I think you misunderstand the Calvinist objection to "free will." Every true Calvinist believes sinners are responsible moral agents, free from any external force or coercion in the choices they make. They choose freely. But they inevitably choose wrong, because their choices are determined by their own nature and their nature is sinful and corrupt. We can discuss this further if you're interested, but the point is simple: A call for the sinner to "choose" something good is in no way incompatible with Calvinist theology.

From Pyromaniacs