Cheers Brother Brad!
(link down below in my signature for said FAQ)
Yes, output of MISI is going to be guitar/instrument level, PA system house mixer INPUT is likely to be MIC level, thus an impedance mismatch, and needing at least a DI box to go into house mixer. If the church has a sound guy, they likely have an 'audio snake' on the stage for all the cables to plug in.
Such a snake is usually using XLR connectors for BALANCED audio to cancel hum and RF interference due to cable runs to the mixer being much longer than a standard guitar cable.
Th iRig Acoustic Stage, as well as the LR Baggs Five.0 AND the MISI are all 1/4" (6.35mm) output and NOT XLR output, as well as UNBALANCED, so you need to go from the instrument into either a DI BOX or preamp/DI with an XLR output....
Something like the Behringer ADI-21 ($39 everywhere) does this handily and on the cheap. and gives you control over your sound in a foot pedal at the stage, otherwise you can spend for the LR Baggs DI/preamps ($149+) or the Fishman Aura or Zoom A3 ($299+) or a RADIAL PZ/DI ($399) or RADIAL TONEBONE ($349).
Others have suggested lots of
good choices.
..but
before going off and spending $300+ on a Fishman Loudbox Mini or Roland AC amp or any kind of preamp/DI box, I would attend at least a few rehearsals with the sound guy present and go with the flow, for if the house mixer out to the PA is done right, you might not need to buy anything....
Also if there is an acoustic guitar player, look at his setup, ask him questions and take some notes as to what he uses in his rig and out to the house PA system.