Halakhah su Deuteronomio 4:19

That He prohibited us from inclining towards idolatry and occupying ourselves with its narratives - meaning to say, into this study of spirituality. [That] means, star x descends according to this description and [then] does such; and [when] they burn incense to y and stand before it according to this description, it does thing z - and that which goes in this way. For thought about these things and study with these [types of] expressions is what arouses a person to seek them and their worship. And the verse that prohibited us from this content is His saying, "Do not turn to the idols" (Leviticus 19:4). And the language of the [Sifra] (Sifra, Kedoshim, Chapter 1:11) is, "If you turn to them, you make them gods." And there (Sifra, Kedoshim, Chapter 1:10), they said, "Rabbi Yehudah says, 'Do not turn to see them'" - it is not even permissible to observe the appearance of the image's form and the thought of its construction, so that one not spend any time [involved with any] part of it. And in the chapter [entitled] Shoel Adam (Shabbat 149a), they said, "[Regarding] writing that is under a picture or under graven images (deyokenaot), it is prohibited to read it on Shabbat. And [regarding] the image itself, even on a weekday it is prohibited to look at it, because it it is stated, 'Do not turn to the idols.' What is the [derivation from this verse]? Rabbi Yochanan said, 'Do not make a god from your minds.'" And the prohibition about this very content - meaning about the prohibition of the thought of idolatry - has already been repeated. And that is His, may He be exalted, saying, "Take heed to yourselves, lest your heart be seduced" (Deuteronomy 11:16). [This] means to say [that] if you have your heart delve into it, it will bring you to veer from the [true] path, and to become involved in its [actual] worship. And He also said about this exact content, "And lest you lift your eyes to the sky" (Deuteronomy 4:19). For He did not come to forbid a person from seeing them with his eyes, but rather forbade the matter in which one relates to their worship with the interest of the heart. And likewise, His saying, "lest you inquire about their gods," is forbidding the inquiry about the nature of their worship, even though one does not worship them. For this all leads to erring about them. And you should know that one who transgresses this is liable for lashes. And this has already been made clear at the end of the first chapter of Eruvin (Eruvin 17b), regarding that which they said, [that] we give lashes for [going outside of] the mixing of perimeters (eruvei techumin). And they gave as a proof, His saying, "let no (al) man go out of his place" (Exodus 16:29); and someone asked and said, "But how can they give lashes for a prohibition, with the word, al, when the commandment did not come with the word, lo? And they answered him rhetorically, "And do we not give lashes for anything that comes with the word, al? But if so, we would also not give lashes for, 'Do not turn to the idols!'" Behold this indicates that we give lashes for this negative commandment. (See Parashat Kedoshim; Mishneh Torah, Foreign Worship and Customs of the Nations 2.)

The oft-cited Tosafot, Sanhedrin 63b and Bekhorot 2b, states only that one may administer an oath to a Christian even though he swears in the name of the Trinity. Tosafot declares that nowhere is there a prohibition against causing gentiles to "incorporate" another deity in an oath. Noda bi-Yehudah Mahadurah Tinyana, Yoreh De'ah, no. 148, carefully distinguishes between shituf, i.e., trinitarianism as a doctrine of belief and an oath in the name of the Trinity. Noda bi-Yehudah declares the former to be idolatry and forbidden to Jew and gentile alike. An oath in the name of a pagan god is forbidden by virtue of the commandment "and in His name shall you swear" (Deut. 10:20). This is, however, an admonition addressed only to Jews. Such an oath is not forbidden to a non-Jew since swearing an oath does not constitute an act of worship. Accordingly, rules Tosafot, a Jew commits no offense in causing a non-Jew to swear such an oath. See also Sha'ar Efrayim, no. 24; Me'il Ẓedakah, no. 22; Teshuvot ve-Shev ha-Kohen, no. 38; Teshuvot Hadashot le-Rabbeinu Akiva Eger (Jerusalem, 5738), addenda, pp. 164-166; Pri Megadim, Yoreh De'ah, Siftei Da'at 65:11 and Oraḥ Hayyim, Eshel Avraham 156:2; and Mahazit ha-Shekel, Oraḥ Hayyim 156:2. Others interpret Tosafot as meaning that shituf or trinitarianism does not constitute idolatry for Noachides. See Rema, Oraḥ Hayyim, 156:1; Darkei Mosheh, Yoreh De'ah 151; Shakh, Yoreh De'ah 151:1 and 151:7; Derishah and Baḥ, Hoshen Mishpat 182; Teshuvot Havot Ya'ir, no. 1 and no. 185; R. Ya'akov Emden, Mor u-Kezi'ah 224; Mishnat Hakhamim, Hilkhot Yesodei ha-Torah; Rabbi Z. Boskowitz, Seder Mishnah, Hilkhot Yesodei ha-Torah and Shoshan Edut (commentary on Eduyot), p. 188; Teshuvot ve-Shev ha-Kohen, no. 38; Rabbi A. Vermeiz, Me'orei Or, IV, 8a and 13a and V, 111b; Revid ha-Zahav, Parshat Yitro; Yad Sha'ul; Yoreh De'ah 151; Teshuvot Sho'el u-Meshiv, Mahadurah Tinyana, I, no. 26 and no. 51; R. Zevi Hirsch Chajes, Kol Sifrei Maharaz Hayes I, 489-490; Ha-Ketav ve-ha-Kabbalah, Deuteronomy 4:19; and Pitḥei Teshuvah, Yoreh De'ah, 147:2. The one early authority who unequivocally rules that Christians are not idolaters is Me'iri. See Bet ha-Beḥirah, Avodah Zarah, ed. Abraham Sofer (Jerusalem, 5725) passim, particularly pp. 4, 28 and 46. See also R. David Zevi Hoffmann, Der Shulchan Aruch und die Rabbinen über das Verhältnis der Juden zu Andersgläubigen (Berlin, 1885), pp. 4-7.

And this negative commandment - meaning, the prohibition of thought about idolatry - is repeated in another place, as it is stated (Deuteronomy 11:16), "Guard yourselves, lest your hearts be seduced and you serve, etc." [This is] meaning to say that if your heart spends much time in thinking about it, it will be a cause to divert you from the straight path and to be involved in its service. And it is also stated about this matter (Deuteronomy 4:19), "And lest you lift your eyes to the heavens and see, etc." As the content [of this verse] is not that a man not lift up his eyes to the sky and observe the heavens, but [rather] the intention of the thing is that he not observe them with his heart's eye - to know their power and their makeup in order to serve them. And [it is] like it is stated in another place (Deuteronomy 12:30), "and lest you inquire of their gods, saying, 'How do these nations serve their gods, and I will do so, me too, etc.'" The verse prevents us from asking about the manner of their worship, since all of this is a cause to err about it.