Does the term “Judaism”, and hence the term “Jews”, come from the name of the Tribe of Judah? If so, why would the name be taken from that tribe as opposed to any of the other tribes? Or maybe the term “Judaism” does not come specifically from Judah?
It is very likely that the term “Judaism” is related to the name of the Tribe of Judah. In Hebrew, the name of this tribe is Yehuda, and a member of this tribe would be referred to as a Yehudi.
If this is the case, one reason why the name of this tribe might have come to be used as the generic term referring to the Jewish People and their religion is due to the centrality of this tribe in the Land and among the People. Judah possessed the central part of Israel, whose territory included Jerusalem and the Holy Temple. In addition, the Tribe of Judah was the monarchal tribe, and the tribe from which the Mashiach will be revealed.
Another possible reason is that Judah was one of the few tribes that remained after most of the other tribes were exiled and lost. When the tribes of the northern part of the Land of Israel were first exiled by the Assyrians, they were dispersed throughout the far-eastern reaches of that empire and came to be referred to as the “Ten Lost Tribes”. When the Babylonians later exiled the remaining tribes in the south of Israel including Judah, Benjamin, Shimon and the cohanim and leviim of the Tribe of Levi who lived among them, Judah was certainly the main tribe. Since these tribes were preserved, most Jews today are considered to be primarily from Judah or Levi.
However, the Talmud (Megilla 13a) presents several sources which indicate that the term Yehudi referring to a Jew is independent of the name of the Tribe of Judah, but rather refers to the fact that Jews repudiate idolatry.
One source is from the Scroll of Ester (2:5-6) which identifies Mordecai as “A Judahite in Shushan the capital, whose name was Mordecai the son of Yair the son of Shimei the son of Kish, a Benjamite who had been exiled from Jerusalem…which Nebuchadnezzar, king of Babylon, had exiled”. The Talmud notes that since the verse states explicitly that Mordecai was from the Tribe of Benjamin, the term yehudi here must not mean Judah. Rather, he was called yehudi because he repudiated idolatry by refusing to bow down to the idol that Haman hung on his neck for the purpose of ensnaring the Jews.
Another source is regarding Chananiya, Mishael and Azariya about whom it is related in the Book of Daniel (ch. 3): “King Nebuchadnezzar made an image of gold…And the announcement was issued…‘O peoples, nations and tongues…you shall fall and prostrate yourselves to the golden image that King Nebuchadnezzar has set up. And whoever will not fall and prostrate himself will be cast into a burning, fiery furnace’…So all peoples, nations, and tongues would prostrate themselves to the golden image that King Nebuchadnezzar had set up…But some Chaldean men approached and denounced the Jews saying, ‘There are Judahite men whom you appointed over the affairs of the capital cities of Babylon, namely [Chananiya, Mishael and Azariya, see verse 1:7]; these men did not take counsel to follow your decree, O king. They do not worship your god and they do not prostrate themselves to the golden image that you have set up’”.
In the continuation of the verses, the king confronts these “Judahites” and threatens them with sure death if they do not comply. To which the men reply, “Let it be known to you, O king, that we will not worship your god, neither will we prostrate ourselves to the golden image that you have set up.” After they are thrown into the burning, fiery furnace but are miraculously saved by an angel of G‑d in front the king’s own eyes, Nebuchadnezzar himself proclaims, “How great are His signs, and how mighty are His wonders! His kingdom is an eternal kingdom, and His dominion is with every generation.”
From here the Talmud notes that even though Daniel himself was from Judah, since the three men mentioned here (Chananiya, Mishael and Azariya) were from other tribes (see Tosafot, Ayin Ya’akov and Sanhedrin 93b), the fact they were referred to as “Judahites” is not because they were from the Tribe of Judah but rather because they repudiated idolatry by refusing to bow down to the idol of Nebuchadnezzar.
A third source, which actually refers to a period that predates the former sources, is regarding the daughter of Pharaoh to whom Scripture refers as a yehudia: “And these are the sons of Bitya the daughter of Pharaoh, whom Mered married. And [Mered’s] wife [Bitya] the Judahitess bore Jered, the father of Gedor, and Heber the father of Soco, and Yekutiel, the father of Zanoah” (I Chron. 4:18). The Talmud explains that the reason Pharaoh’s daughter, who certainly was not from the Tribe of Judah, is referred to as yehudia is because she too repudiated idolatry. How so? The day that she went to bathe in the Nile (Ex. 2:5), she ritually immersed herself in order to become “cleansed” of her father’s idols.
So while the term “Judaism” most probably is related to the name of the Tribe of Judah, Jewish sources indicate that it is no less, and perhaps even more significantly, related to Judaism’s denial of idolatry and its proclamation to the world of the belief in the One G‑d of Israel.