Christ instituted only one church, and
that society was both formally and
specifically a visible one.
"I pray not only for them (the Apostles), but also for those
who will believe in me through their word, so that they
may all be one, as you, Father, are in me and I in you,
that they also may be in us, that the world may believe
that you sent me."
"... upon this rock I will build my church" (Both "this
rock" and "my church" are clearly singular in the Greek
I have other sheep that do not belong to this fold. These
also I must lead, and they will hear my voice, and there
will be one flock, one shepherd.