There are many issues involved in the story of the akeida. In this post, I wonder what happens when one combines 2 classical questions.
ויהי אחר הדברים האלה והאלהים נסה את אברהם ויאמר אליו אברהם ויאמר הנני
ויאמר קח נא את בנך את יחידך אשר אהבת את יצחק ולך לך אל ארץ המריה והעלהו שם לעלה על אחד ההרים אשר אמר אליך
So begins the parsha of the Akeida. G-d tells Avraham to sacrifice his son, and then just as he is about to do it, G-d tells him:
אל תשלח ידך אל הנער ואל תעש לו מאומה כי עתה ידעתי כי ירא אלהים אתה ולא חשכת את בנך את יחידך ממני
Question One: How could G-d go back on His word? If He said that Yitzchak should be slaughtered, how could He then say “Just testing!”? G-d's word is Truth!
Answer: G-d didn't tell Avraham to slaughter Yitzchak, He just said “ha'alehu sham l'olah”, a somewhat ambiguos command that doesn't necessarily include slaughtering. Once Yitzchak was put on the mizbeach, that was enough. The command was fulfilled, and Akeidas Yizchak became an everlasting merit for our people.
Question Two: What was the big test for Avraham? G-d commanded him directly to bring his son as a korban! How could he have ignored a direct Divine command?
Answer: Avraham could have come up with some powerful arguments to not listen to the command. “G-d commanded man never to murder, how could I kill my own son? Moreover, G-d promised me that Yizchak will become a great nation, when he said:
ויוצא אתו החוצה ויאמר הבט נא השמימה וספר הכוכבים אם תוכל לספר אתם ויאמר לו כה יהיה
זרעך
and some time later..
כי ביצחק יקרא לך זרע..
..it can't be that I should kill him!” But Avraham listened to G-d and went to slaughter his son. He passed the test.
Now, does everything make sense? But one second..
...Question: If G-d just meant Yitzchak should be put on the mizbeach, why did Avraham pull out a knife and get ready to kill his son? Didn't he know that you can't murder? Didn't he know the promise? If in truth, G-d's command just meant put him on the mizbeach, why did Avraham try to do so much worse?!
For Further Emphasis: If G-d really meant for Avraham to kill Yitzchak, we understand why Avraham tried. But then how could G-d have changed His mind? And if G-d actually used a truly ambiguous command, then why did Avraham interpret it to mean something so crazy?
Answer: “Ha'alehu..” cannot just mean put Yitzchak on the mizbeach and take him down. Thats not what the words mean. It says “l'olah”! Putting Yitzchak on a mizbeach and doing nothing is nothing. “Ha'alehu” means put Yitzchak up as an olah, with full intentions to slaughter him just like an olah.
Avraham had to realize that when G-d commanded him to bring Yitzchak as an olah, He meant it. It was docheh any prohibition or promise from before because it was a direct command from G-d. Avraham didn't know what would happen, but he realized he would have to bring his son as a genuine olah.
Avraham traveled to the mountain and went up with Yitzchak and put him on the mizbeach. Then Avraham tied Yizchak down. Then he pulled out a knife, ready to slaughter his son. Only now, at this moment, did G-d say
אל תשלח ידך אל הנער ואל תעש לו מאומה כי עתה ידעתי כי ירא אלהים אתה ולא חשכת את בנך את יחידך ממני
Until Avraham showed he was totally ready to actually sacrifice his son, “Ha'alehu sham l'Olah” was not fulfilled. But once avraham raised the knife, it showed he had actually brought Yitzchak as an Olah. He hadn't slaughtered Yitzchak, but the command had been fulfilled. Yitzchak became a complete Olah, and the “ashes of Yitzchak” become an eternal remembrance before G-d. Avraham had fulfilled the nisayon of “Ha'alehu sham l'Olah”, no murder had been committed, and now Yitzchak could truly grow into the great nation of the promise:
ויאמר בי נשבעתי נאם יהוה כי יען אשר עשית את הדבר הזה ולא חשכת את בנך את יחידך: כי ברך אברכך והרבה ארבה את זרעך ככוכבי השמים וכחול אשר על שפת הים וירש זרעך את שער איביו: והתברכו בזרעך כל גויי הארץ עקב אשר שמעת בקלי
