When G‑d asked Abraham to take his son, his only son, the son he loves, Isaac, and raise him for an offering upon a mountain, G‑d said, “please.”

He said, “Please stand for me in this test, so they will not say, ‘The other tests were of no substance.’”

The other tests included being thrown in a fiery furnace for not worshipping Nimrod.

Not complaining when he had to leave the land promised him so as not to starve.

Not flinching with fear when he ran to save his nephew from the powerful armies that had captured him.

Not wavering from his faith when he had been promised many children and not a single one had been born.

And all this would be unsubstantial if he would fail this one test?

Yes. Because all these tests only demonstrated that Abraham was a man with a cause.

A man with a cause identifies with his cause. He is obsessed with his cause. He could give his life for his cause.

Avraham himself did not know: Was he doing this because it was his cause, or purely because it was truth?

Until a challenge came that would not promote his cause, not affirm his identity, not contribute to his future, or any future. Something that could only burn down everything he had ever built. 

But it was truth.

When Abraham fulfilled that impossible act, G‑d said, “Don’t do anything to the lad. Because now everyone will know that all you do is real.” 

Likutei Sichot vol. 20, pg. 73ff.