This portion of the Torah narrates a tragic event. Within weeks of the greatest spiritual event of history, the Divine revelation at Sinai, the Jews, who had reached a level of angelic holiness, fell precipitously into the idolatry of the Golden Calf. How could so radical a change occur?
Rabbi Chaim Shmuelevitz explains that when Moses failed to return at the designated date, after forty days on Sinai, the people thought he had died. They were in a barren desert, with no evident source of water. Their only trust was that Moses could intercede for them with G-d, and if Moses was dead, they were trapped in the arid desert. They panicked, and in a state of panic, one may lose all ability to reason, and one may commit the most absurd acts.
This is a crucial teaching. Logical thinking can serve us well, but if we panic, we lose the ability to reason logically, and we may do things that are grossly out of line with our spirituality.
We may be subjected to severe stresses, but we must try to avoid panic.