Just like Biblical criticism does not mean to criticize the Bible, textual criticism does not mean to criticize a text. It just means to try to look at a text (in the case of the Bible, the Biblical text) in a critical/scholarly/objective way. Specifically, textual criticism means looking at several different really old copies of the Bible, noticing when there are differences among them, and trying to determine which one makes the most sense in each case.
One of my favorite examples of textual criticism of the Bible answers a famous question often heard at the Passover Seder. In the Hagadah (the text used during the Seder), we are taught that the Torah teaches us about four types of sons who attend the Seder, two of whom are the wise son and the wicked son. What differentiates the wise son from the wicked son? The wicked son asks, “What is this service of yours (Exodus 12:26)!” The Hagadah explains that he is wicked, for he said, “of yours,” implying that he wants no part of the Seder and his people’s traditions. The wise son, for his part, says, “What are the decrees, laws, and rules that YHWH our god has commanded you (Deuteronomy 6:20)?” So he’s showing interest.
But wait: the wise son also said, “What are the decrees…. That YHWH commanded YOU!” He’s excluding himself, just like the wicked son did! So how does he come out being the good boy?
While many of us have heard responses to this question, I think it’s safe to say that in most cases, “The question is better than the answer,” as we’d say in yeshiva.
So a textual critic asks, “Wait a minute; what if the text that the original Hagadah had was slightly different from what we have in our Hagadah’s today, and maybe that slight difference would explain the apparent contradiction here?” Turns out that modern scholars who have looked at some of the various old copies of the Biblical text, including other old texts that cite the Biblical verses mentioned above, have found a very important difference!
As Jeffrey Tigay, Ph.D., professor emeritus at the University of Pennsylvania, shows in his wonderful article (here) on the Bible codes, this passage about the four sons appears in the Jerusalem Talmud (Talmud Yerushalmi) and the Mekhilta (a compilation of rabbinic discussions of some of the legal parts of the Pentateuch), and both quote the wise son’s statement with a change in one word. Instead of “What are the decrees, laws, and rules that YHWH our god has commanded you (eschem)?” these ancient sources quote the wise’s son question, which is a quote from Deuteronomy 6:20, as: “What are the decrees, laws, and rules that YHWH our god has commanded us (osanu)!” In addition, the Septuagint, the ancient Greek translation of the Bible, also has “us” in this verse, rather than “you,” suggesting that the Hebrew Bible used when making the Greek translation also had “osanu (us).” Thus in the original Hagadah, the wise son does not, in fact, exclude himself by saying, “the laws that God commanded you,” and so that’s why he’s not the wicked one.
And so modern Biblical scholarship, in this case textual criticism of the Bible, has answered a long-standing question, asked mostly by people who would consider textual criticism heretical. :) But seriously, how could anyone find this heretical! Some of the best textual critics of the Bible are/have been Catholic priests, because they want to figure out the most accurate version of God’s word. Why can’t Orthodox Jews adopt the same attitude?