The last conversation between Moses and Joshua began as a gift and ended as a rebuke.
On the day Moses was to enter Paradise, he turned to his closest student and said, "If any doubtful matter remains, ask me now. I will explain it. Do not wait until I cannot answer."
Joshua, hurt perhaps by the thought of separation, answered with a flash of self-defense. "Have I ever left your side for an hour? Did you not yourself write of me — his servant Joshua, the son of Nun, a young man, departed not out of the Tabernacle (Exodus 33:11)? How could I have any doubtful matters?"
It was the wrong reply. Instead of receiving the offered instruction, Joshua deflected it back at his teacher. The Holy One withheld nothing from Moses — but He withdrew something from Joshua. In that instant, three hundred halakhot fled from Joshua's mind. Seven hundred doubts rose up in their place.
All Israel, when they realized their new leader could not answer the questions they brought him, rose to attack him. They thought they had been given a lesser teacher.
But God intervened. "To restore those laws to your memory," He said to Joshua, "is not possible. But go, occupy them with work." The Book of Joshua opens at exactly this moment: Now after the death of Moses, the servant of the Lord, it came to pass that the Lord spake unto Joshua (Joshua 1:1), and God sent Israel to conquer a land.
Temurah 16a preserves the lesson. When a teacher offers, receive. When a student posture, he loses.