David Archuleta made a pretty big announcement about his personal life at a concert in Utah last night ... but to people who know the guy, it probably wasn't that shocking. The former "American Idol" runner-up told his home crowd ... that he's ... (wait for it) ... putting his music career on hold for two-years to fulfill a full-time mission with the Mormon church!! The announcement was pretty emotional -- with the crowd erupting in cheers ... and David breaking down and crying on stage. 20-year-old Archuleta explained, "It's not because somebody told me that I was supposed to do it, not because that I no longer want to do music anymore, but it's because it's the feeling that I felt that I need to do next in my life."