In the year 2448 from Creation (1313 BCE), Tammuz 16 was the 40th day following the Giving of the Torah at Mount Sinai, and the people of Israel wrongly expected Moses' return from the mountain (he would actually return on the following day). When their leader failed to return, they demanded from Aaron: "Make us a god that shall go before us". Hur (Moses' nephew, the son of Miriam and Caleb) tried to stop them and was killed by the mob. Aaron fashioned a calf of molten gold.
Links:
The Making of the Golden Calf (text of Exodus 32 with Rashi's commentary)
An anthology of Midrashim and Commentaries on the making of the Calf
The Day Before (on the deeper significance of Tammuz 16, from the teachings of the Lubavitcher Rebbe)
More on the Golden calf
See also "Today in Jewish History" for tomorrow, Tammuz 17.
There are those who say that before we do any mitzvah, we must first understand why it needs to be done. Why else were we given a mind?
There are others who say we must just obey with simple faith. How else can we bond with One who is entirely beyond our understanding?
Abraham did both. He began with absolute faith, even when it was impossible to make sense of what he had been told to do. Yet he would not leave until his questions were answered and he had been given a way to understand.
“Don’t do a thing to the young man, for now I know that you are a G‑d fearing person.” (Genesis 22:12)
Abraham said to G‑d, “Let me present my case. First You told me that my descendants will be from Isaac. Then You told me to take him for an offering. Now You say I mustn’t do a thing to him…” (Rashi, citing Midrash)
That makes sense. Matters that are beyond our understanding can never be fit neatly into human reason. But neither can they be left in conflict.
Because if what you believe is true, it must be true everywhere. Even within your own limited human mind.