Missionaries from the Stars

Sending missionaries to convert Native people in "discovered" lands to the conquerors' religion has been common on Earth for thousands of years. But how might Earth receive missionaries from another planet who arrived to convert Humans to the interplanetary religion?

Missionaries from a planet 30 trillion miles away arrive on Earth. They conceal their reason for coming at first. Humans find the mysterious arrivals to be compelling, but they aren't sure why.