It's just a different conclusion about its origins. Some people think that the entire Bible is the word of God, others believe it be a historical product, and others believe it contains legends and myths that point towards God. I seems just as rational to ask, "why would anyone believe this was an actual event?"
But that is what I am asking. Do you think it is? Why? And what does the story mean to you?
It was an actual event, but realize this:
The story of Abraham and Isaac is the foretelling of how God would be the one to sacrifice his beloved son for us, as you see in the story of Abraham and Isaac, God supplied the ram for the sacrifice at the last minute.
A ram represents a full grown male, as opposed to a lamb.
It is a foretelling of what God would do for us, but it was accredited to Abraham as an act of great faith in The Lord.
It seems Abraham believed he was being punished for loving Isaac more than Ishmael, and/or not trusting God in the first place and having sex with Hagar (who was not his wife) in order to concieve Ishmael. Then Isaac of the promise was born.
However, the story of Abraham and Isaac is the foretelling of how God would sacrifice his only begotten son, Jesus, for us.
God always connects something, one needs to keep seeing the connections.
It's paramount to understanding scriptures.
Hope that helped explain what the meaning of Abraham and Isaac is, and why Christians are now the spiritual seeds of Abraham.
This is part of the reason the Bible says The God of Abraham, Isaac and Jacob. As far as why Jacob is included is Jacob's lineage through his son Joseph who was sold into slavery in Egypt by his brothers, comes the line of Judah, which is the lineage of Christ. And the story of Abraham and Isaac is explained above.