The command is very unusual. Imagine if you were Abraham and God commanded you to offer as a sacrifice (to kill) the very one whom God had promised you would be the heir to His promise. Abraham, through faith, reasoned that God would resurrect Isaac because Abraham knew that God was righteous (that God was faithful to His word). But God had other plans.I think the foreshadowing of the cross is probably the clearest element of this story, and I know it's important to keep that in mind at all times.
I also recognize that perhaps I chose poor wording with "moral justification." I mostly meant to ask how this situation fits with God's character, as revealed in the Bible. On its face, the command seems very unusual, and I was simply seeking a solid answer for my own sake and for the sake of others who might raise the question with me.
The only satisfactory answer that I can give you insofar as Abraham's obedience in the face of
God's command is to obey regardless as to our reasoning or our theologies. Faith is obedience regardless of the command suiting our rationale. This was the faith of Abraham. God commanded it - do it. Regardless of our expectations God will work it for the good. Notice....Abraham's expectations were wrong, but his faith was not misplaced.