Christians are the new covenant people of God.
"But you are a chosen generation, a kingly priesthood, a holy nation, a purchased people: that you may declare his virtues, who hath called you out of darkness into his marvelous light" (1 Peter 2:9)
For the sake of the old covenant, the official policy of traditional Christianity toward Judaism is toleration, beyond that extended toward Muslims or pagans. However, there is no traditional Christian endorsement of post-messianic Jewish religion, since Christ is the sole means of salvation. Christians are under no obligation to take sides in external religious disputes among Muslims, Jews, or pagans.