The Law vs Faith

God does not want our faith to be in obedience to the law, but rather in the truth of His Word/Promise. What He has promised He will do, He will do, because when we believe in our self-effort we believe in ourselves, but when we believe in the authenticity of His Word, we believe in Him, this is why the law and gospel are two different concepts, they cannot be mingled. 

That was the kind of faith Abraham had in God, the faith that believes in God's promise.  What Paul is calling FAITH in this context (Romans 4:13-16) is Faith in God's promise simply because He (God) cannot lie, because it still requires faith to accept the law and try to follow it, but the end of that is faith in ourselves (our ability, and obedience).

 Without faith in God's promise based on who He is, faith is pointless. We obviously should know God is perfect and we are not, the law shows us this over and over again, so it is far better to believe in God and only God without dragging ourselves into the equation. 

The message/promise “In they seed shall all the nations of the Earth be blessed” is a promise for all nations through faith and not for one nation through the law. So, if only one nation would receive this blessing, the promise for all nations is no longer relevant.