I was interested in the issue of idolatry and thus learned Sanhedrin 64 and onwards until the next chapter, and also that Tosphot on shituf שיתוף. Shituf שיתוף is combing the name of God with another. This comes up in the Gemara and right there on the page Tosphot deals with Christianity. To Tosphot it is not idolatry since they worship God, but they join God with a representative. So it is shituf שיתוף.

at least that is one opinion in tosphot. but when i learned that tosphot with david bronson, he noticed that there seemed to be a few other approaches in that very same tosphot.

At any rate, the problems with Christianity are (bitul hamitzvot) nullification of the commandments -which comes from Paul, not Jesus. The other is worship of a person who is not the first cause. that is wrong even given that he was the Messiah son of Josef as held by Rav Avraham Abulafia. a person being considered ''divine'' is not against the torah as stated by the Ari Rav Izhak Luria about Avraham, Izhak yaakov and others who were souls of Emanation which is totally Godliness.