The Mormons differ from Orthodxx christianity in their beliefs about Christ."
Do you think that matters to the Jews or to God if The Church of Jesus Christ of Latter-Day Saints is considered by you to be "Christian"?
Do you think that: (Genesis 12:3) "And I will bless them that bless thee and curse him that curseth thee; and in thee shall all nations of the earth be blessed" -- applies only to your narrow definition of Christian?
My best friend is Jewish and I am appalled at what "Christians" have said to her and treated her. If I weren't there at the time, I don't know that I would have believed the blind ignorant bigotry myself.
God through his Word has commanded His people to test the spirits since there are false teachings and false teachers.
It would be irresponsible not to do so. Since Mormons do not profess the truth about the nature of God and claim they will be gods themselves, they are not Orthodox, though they claim to be.