The Akeida Is A Test?

I don't understand why the Akeida is such a nisayon for Avraham Avinu. I mean, I get it that the first time it was hard. But EVERY YEAR?? He already knew from the first time that he wouldn't have to sacrifice Yitzchak. If I already know the ending from previous years - then Avraham Avinu CERTAINLY knew!!!!