A friend, still cross at the Mormon Glenn Beck for telling Christians to leave their churches, wrote last night asking if Mormonism is a form of Christianity or another religion, and I would be grateful for your thoughts.
There are a couple of tests, it seems to me. One is the teaching of the major Christian traditions on Mormon baptism, which as far as I know is universally negative. See Why Mormon Baptism is Invalid for the Catholic position. If the baptisms are not Christian baptisms, the baptized are not Christians.
That settles the matter for me, but there’s a second test to which the answer is also no. That is whether Mormonism can be considered a Christian heresy. We know it’s not orthodox Christianity, but is it close enough to count as a form of Christianity? A Lutheran friend suggested that it is, but I don’t think so.
A rough test is that heresies 1) begin with a man of some weight and authority in an obviously orthodox or mainstream form of Christianity; 2) tend to go bad in one direction and at one point, that is, they take one doctrine and deny it or exaggerate one aspect or try to improve it in some other way; and 3) argue with some plausibility from Scripture and tradition. Arius was a churchman, for example, and left the Faith alone except for his assertion that Jesus was a creature, which he insisted (and not without reason) was what Scripture says.
Mormonism is not a heresy. It did not begin with a man of authority nor in a mainstream form of Christianity, it did not twist an existing doctrine but invent a whole bunch of them, and it argued from personal revelation rather than Scripture and tradition, which it treated with some creativity. It is not a heresy, it is a different religion.
What the Christian does with that, and where in the array of interfaith relations we place Mormonism, is another question.