Nobody knows the answer save Allah. What we know is a matter of deduction from the available literature or interpretations.
What is commonly believed is that nothing syirk will be tolerated by Allah and the Christians already indulge in syirk (belief in the trinity). However, that is not to say that they 'heart' is not in the right place, like charity. The Jews, they believe in monotheism (Allah likes that) but have no charity in their hearts....
I'm not sure about going to hell for taking Jews as friends, but what it is trying to say is that they cannot be depended upon as friends or ally, like the time of the prophet (pbuh) when the Jews kept playing him out when they were called to honor their pledge.
Peace