Abraham :: obedient and faithful

Read Genesis 22 this morning - the story of when God tells Abraham to take his only son (and note how God says 'the son you love') and sacrifice him. The thing that struck me was that Abraham was so obedient and had so much faith in God that he just did it. God only had to give this command once!! How many of us, had we been told to do that, would've gone 'are you sure God? I mean, is this really necessary?!' I know u would've done that! But Abraham gets told once, and he does it. Now that is a challenge!!