Abraham trusted God with all his heart and had so much faith in God's promise to Him...that he put it into action. He set out to sacrifice his son who had been a miracle seeing Sarah was 90 years old when he was conceived. God had told Abraham that through this seed he would be blessed. Abraham believed God and had that much trust in Him that he was willing and set out to do what He said.
Now, if he hadn't have believed and trusted and would have told God no, then we would have probably never heard of Abraham because he would have had a dead faith, and probably wouldn't have been called the friend of God. I mean, if we go by what the scripture actually says, anyhow.
James 2
19 Thou believest that there is one God; thou doest well: the devils also believe, and tremble.
20 But wilt thou know, O vain man, that faith without works is dead?
21 Was not Abraham our father justified by works, when he had offered Isaac his son upon the altar?
22 Seest thou how faith wrought with his works, and by works was faith made perfect?
23 And the scripture was fulfilled which saith, Abraham believed God, and it was imputed unto him for righteousness: and he was called the Friend of God.
24 Ye see then how that by works a man is justified, and not by faith only.
This scripture has nothing to do with what men think about faith without works, but it does have everything to do with what God thinks about it.
Now God sent his Son and sacrificed Him for our sins. All he wants us to do is belive in Him and put our faith and trust in Him and let Him work in and through us.