And it came to pass after these things that God tested Abraham (Genesis 22:1). Rabbi Yochanan, speaking in the name of Rabbi Yossi ben Zimra, asks in Sanhedrin 89b: after what things?
After the words of the Accuser. The Accuser — Ha-Satan, the angel whose task is to press Heaven's hard questions — stood before God and said, "Master of the Universe, You gave this old man a son at a hundred, and at the feast of the child's weaning he did not even spare a single dove to sacrifice to You." God answered, "He made the feast for his son's sake, and yet I know he would not refuse to offer that very son at My command."
So the test began. But notice how God phrased it. Not "take him" and be done. "Take now thy son." Abraham says, "I have two sons." "Thine only son." "Each is the only son of his mother." "Whom thou lovest." "I love both." "Isaac." Step by step, God walks Abraham into the full weight of what is being asked — the way a general might say to his most decorated warrior, "Fight this one battle hardest of all, so that no one can call your earlier victories luck."
And then, on the road to Moriah, the Accuser comes in person. He twists the words of Job against Abraham. "Shouldn't such trials be beneath a man like you? You have instructed many and strengthened weak hands — and now this?" Abraham answers with words the Psalmist will later speak (Psalms 26:11): "I will walk in my integrity."
Every step is a chance to turn back. Abraham walks on. The test was never whether he would sacrifice Isaac. The test was whether, question by question, he would keep walking.