Here's a nice quote: "Muslim activists are finding out why getting into a negative-publicity fight is as inadvisable as wrestling with a pig: You get dirty and the pig enjoys it."
That saying also pretty well fits some of the verbal exchanges on this forum.
Turn your sentence 180 degrees around, and it becomes:
"I believe in Allah and I know that Christianity is a false religion, because if Christianity were true, that would render all that I know about Mohammed a lie."
Can you imagine how many people on earth really do accept this?
Both statements cannot be true, thus, per Occam's razor, neither is.
BTW, Christianity is actually a minority, when you compare it to the entire world population of 7 billion: