Was Bar Mitzvah some sort of ancient rite of passage that's been lost?

No. As Mark Oppenheimer documents in his book Thirteen and a Day, there is no mention of Bar Mitzvah in the Torah or the rest of the Bible. The Talmud does not mention thirteen as an age of significance. It is not until the Middle Ages that this moment in a young man’s life was seen as important.

No one has - yet - unearthed some ancient, mysterious glyphs or papyri that contain coded descriptions of some majestic rite-of-passage ritual through which Jewish boys became Jewish men.

Honestly, such a ritual may not have been needed back than. But it is certainly needed now! Now, when what it means to be a man is so unclear to most men; when male role models are harder to come by; when many fathers feel utterly confused about how to relate to their sons; when rabbis are distant; when Jewish life seems irrelevant - now is when we need a rite of passage through which Jewish boys become Jewish men.

Because we need good men out there who are knowledgable, wise, humble, brave, curious, strong, resourced, connected, responsible, energized and joyous. We need men out there who have vision, self-awareness, the capacity to reflect, and therefore, to grow.

So, we take Bar Mitzvah - no one was doing much with it anyway - and we make it the place-holder for a new Rite of Passage. It is open to the needs of our times. It can be nudged in many different ways in order to carry the meaning we need it to carry.