Is Christianity Shituf or Avodah Zarah?
Rabbi Moshe Sternbuch, chief of the Edah HaChareidis rules that Christian denominations that believe Yeshu ימש״ו is the incarnation of G-d chas v’shalom, fall under the category of actual Avodah Zarah and are not considered Shituf/"partnership" (link - link).
“Christianity is not merely Shituf, which according to some opinions gentiles aren’t warned against, in truth they corporealize our G-d blessed be He, through their idolatry with the title “son” ר״ל, the gravest form of idolatry." (Teshuvos VeHanagos siman 317)
(Since there is a prohibition against learning the ways of Avodah Zarah (Rambam, Avodah Zarah 2:2, Shulchan Aruch, Yoreh Deah 139) don’t open the links below without consulting a Rov.)
There is a common misconception amongst Yidden regarding mainstream Christianity, i.e. trinitarian Christianity. Their deity is not a sort of tritheism with G-d at its head. That would actually constitute heresy in trinitarian Churches. The Trinity is a “homoousion”, the belief that G-d is three distinct hypostases or persons who are coeternal, coequal, and indivisibly united in one being, or essence. In fact, that is why (link - link) they falsely claim to be monotheistic. In order to reconcile their three G-ds with the one G-d of the Torah they just combined them into one and called it a paradox. Even according to the opinions based on Tosafos to Bechoros 2b Sanhedrin 63b that shituf(1) is permitted for Bnei Noach, this doctrine should be actual Avodah Zarah. They don’t believe in some sort of partnership of false deities with the Creator or as intermediaries between them and Him. They redefined Him as composed of three primordial equal parts chas v’shalom, one even having form, i.e. Yoshke ימש"ו.
(1)One clear example of the definition of Shituf: The Rama OC 156 quotes Tosafos 63b “sh’mishtatfin shem shamayim v’davar acher”, the Olas Tomid on this Rama says:
“klomar sh’omrim d’ze l’mala mize (they recognize Hashem is above they’re AZ) veinam pogmim b’yichud Hashem (and they don't compromise Hashem's unity), omnam im pogmim b’yichud v’omrim sh’shnayim hem, ze bichlal AZ”.
Meaning if they believe it’s literally a partnership then it would be AZ (how much more so if they believe they’re one essence). Others limit shituf even further (See Sefer Hamamarim Melukat 1 p.323, Mamar Mayim Rabim 5717, Melukat 3 p. 128 B’yom Ashtei Asar 5731 ibid footnote 20)
In other words, they would have been better off believing in a sort of tritheism than redefining G-d in this preposterous form (although as quoted above from Rav Sternbuch, by claiming Yoshke is the embodiment of G-d and not merely another deity, they are anyway corporealizing Him). Shituf is permitted according to some opinions, but only as long as they also believe in Hashem according to our definition. How is this doctrine any different from that of the Greek g-ds with Zeus as the chief deity of the pantheon with Yoshke instead? In conclusion, the Trinity is the Christian version of the pagan pantheons of antiquity and is pure Avodah Zarah.
It should be noted though, the Lubavitcher Rebbe in a handwritten editing remarks to a letter
“Christianity is Avoda Zara, is in contrast to the seven Nohadite laws, as opposed to Islam. However, the Christians of today are simply “Maaseh Avoseihem Beyadeihem”.
Accordingly, the average layman may not be considered an idolator.
Survey - A Majority Of Americans Think J Is A Great Teacher Yet Reject His Claims To Be G-d
Halachic Ruling by Rav Sternbuch
(Nontrinitarianism rejects the doctrine of the Trinity. The din of such churches depends on their respective beliefs)
Another point worthwhile of discussion is whether the Christian doctrine of the abrogation of the “Old Testament” by the “New Testament” ח"ו disqualifies adherents of Christianity as Pious Amongst the Nations. It is a prerequisite of the 7 Noahide Laws that Gentiles bide by them because it says so in “the Torah of Moses”. (Rambam, Hilchos Melachim 8:11. Likkutei Sichos vol. 26 p. 132.) However, that is beyond the scope of this paper (possible answer).
(audio shiur on shituf based on Tosafos to Sanhedrin 63b)
האמונות והדעות לרבנו רב סעדיה גאון
תשובות והנהגות להרב משה שטרנבוך
האם הנוצרים בימינו עובדי עבודה זרה הם?