So, indulge me on this little hypothetical...
Suppose I didn't know which church was true. Suppose I didn't have a testimony that the church I belong to is Christ's one true church here on earth. And suppose I was looking for His church. And all of a sudden one day this* shows up hanging on the door to my apartment:
Um... I think I'd keep looking.
*Yes, this is real. That is a man with his pants around his ankles on a flyer for a church. Called "Naked Church". And their slogan is "Taking it all off". I am not making this up.