Terach is seemingly a bit player in the Torah. Mentioned only in a few verses, he seems to be of little significance, except as the father of Avraham.
But as others have pointed out, Terach must have been someone quite important. We know that Terach had three sons: Avraham, Nahor, and Haran. All of those sons ended up becoming part of the Jewish people: Avraham was, of course, the founder of Judaism; all of our foremothers, Rivka, Rachel and Leah, were Nahor’s descendants; Sarah, Ruth and Naama were descendants from Haran. So every one of Terach’s children had Jewish offspring.
Why? What made Terach so special? Why is he such a great man that, alone among all the people in the world, Judaism came from every single one of his offspring?
The answer is hidden in plain sight:
And Nahor lived twenty nine years, and fathered Terah; And Nahor lived after he fathered Terah a hundred and nineteen years, and fathered sons and daughters. And Terah lived seventy years, and fathered Abram, Nahor, and Haran. (Gen: 11: 24-26)
Terach does something nobody had ever done before: he gave his son his father’s name.
We must not underestimate the magnitude of this. If we look at a line of gravestones in any Jewish cemetery in the world, every family line shows the connection between the past and the future through the repetition of names: from grandparent to grandchild, great-grandparent to great-grandchild. We use names as the link between the past and the future, the anchoring of new life in the solid foundation of those who have come before us. It is how we, as Jews, keep the flame and memory of our ancestors alive, by giving them an ongoing stake in the future.
And this is the very first thing the Torah tells us about Terach. He may have been, in all other respects, an idol-worshipper, but this single act made all the difference. It is why Avraham, and then Isaac and Rivka insist on their children marrying other descendants of Terach. Because to be a Jew means to be connected to thousands of years of our ancestors, and to be their link in the chain to the future. By giving a name that comes from our past, we proclaim that our lives, and our mission, do not stand alone.
This is why the first book in the Torah ends with the beautiful story of Yaakov blessing his grandchildren, Ephraim and Menasseh. The story of the Jewish family starts with a man naming his son after his father. And the end of this story, just before the Jewish people start to become a nation, is marked by the grandfather directly skipping a generation, explicitly bonding a grandfather to his grandsons.