Indeed, we see the early existence of the Church in the election of the Apostles and their sending forth:
he called the twelve; and began to send them two and two, and gave them power over unclean spirits... (Mark 6:7)
As any living organism, the Church grows and develops from assembly of the elect to the functioning image of heaven:
if he will not hear thee, take with thee one or two more: that in the mouth of two or three witnesses every word may stand. And if he will not hear them: tell the church. And if he will not hear the church, let him be to thee as the heathen and publican. Amen I say to you, whatsoever you shall bind upon earth, shall be bound also in heaven; and whatsoever you shall loose upon earth, shall be loosed also in heaven. (Matthew 18:16-18)
In contrasting these two quotes we see development from a group of disciples organized in twos to something that is a higher instance than two disciples, and already called "the Church". Yet both stages were achieved before the Pentecost.
Thank you.