Once you complete The New Kid in Town, you'll be able to explore South Park. In front of the City Hall building is Priest Maxi sitting on a bench. Talk to him and he will tell you to find Jesus, who is actually hiding inside of the Church. To get there, head west two screens and it will be right in plain sight.
Go inside and you'll see that Jesus is popping up and down in the middle pew on the right side of the church. Go into the middle pew and talk to Jesus, and you'll have to go back to Priest Maxi again, who tells you to go and find Jesus one more time. Head back to the Church and you'll have to solve a little puzzle before you can find Jesus again.
There should be two lights in front of the podium that you can interact with; turn both inwards so they shine above the podium. Once you do that, you can turn off the church lights using a switch by the door on the right side, which when done will show Jesus' shadow hidden behind the podium. Talk to him here to finish this sidequest and get both Jesus and Priest Maxi as friends, as well as an item to summon Jesus in battle.
