Having many Chabad Lubavitcher friends, this is no threat to Christianity. The Chabad folks are typically the ones "behind" the 7 Noahide Laws (which have been around much longer than Christianity).
Incidentally, they teach that Gentiles who follow the 7 Laws have a place in the World to Come. Thus they are NOT trying to convert people to Judaism, nor away from Christianity! The Rebbe ("Blessed be he, the Lubavitchers would state) stated such in the 20th Century, and the previous Lubavitcher Rebbes spoke in similar terms. So no, this is not of concern to Christians.
There are fringe people out there, such as John Stone who are very anti-Christian. But John Stone is not Jewish, nor does he claim to be (although he sure wants to be!).

Grace is not common.