I think we would all agree that the English word “church” originates from the Greek word, “Ecclesia”. Without going into great detail I believe that we can also agree that this Greek word basically means “assembly.”
Ok, if we agree so far then we can move on to what assembly we are referring to when discussing the word, “Church.” I think it logical to begin with the promise of the church.
We find the promise here: Mat. 16:18 And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it.
In this promise Jesus defines what church he is talking about; He said it would be his church and that he would build it. If we take Jesus at his word we can eliminate any other church, or assembly, if you will. We can also affirm that his church did not exist before this because the words “I will build” are in the future tense.
We find the first members of his church mentioned here” 1Cor. 12:28 And God hath set some in the church, first apostles, secondarily prophets, thirdly teachers, after that miracles, then gifts of healings, helps, governments, diversities of tongues.
We find that he chose these apostles here: Luke 6:13 And when it was day, he called unto him his disciples: and of them he chose twelve, whom also he named apostles.
Since the office of apostle is then a “church office,” we can safely say that when he chose the twelve this is the beginning of “his church.” There are many scriptures that show that his church was in existence during his personal ministry on earth. They do not show the time of the actual beginning, but they affirm that it existed at that time. There is no scripture that comes right out and says; “The church began at this time.”
There are many that think that the church began on the day of Pentecost. But a serious study will show that the church existed before Pentecost. I’ll just mention a few here. Jesus is with his disciples here as they partake of The Lord’s Supper: Mat. 26:29 But I say unto you, I will not drink henceforth of this fruit of the vine, until that day when I drink it new with you in my Father's kingdom.
30 And when they had sung an hymn, they went out into the mount of Olives.
He sang this hymn with them in the midst of the church: Heb 2:12 Saying, I will declare thy name unto my brethren, in the midst of the church will I sing praise unto thee.
The Lord’s Supper is a church ordinance.
Just the fact that they partook of The Lord’s Supper presupposes that there is a church in existence at this time.
The authority of disciples in church capacity was placed in the church during Christ's earthly ministry. Mat 18:15. Moreover if thy brother shall trespass against thee, go and tell him his fault between thee and him alone: if he shall hear thee, thou hast gained thy brother.
16 But if he will not hear thee, then take with thee one or two more, that in the mouth of two or three witnesses every word may be established.
17 And if he shall neglect to hear them, tell it unto the church: but if he neglect to hear the church, let him be unto thee as an heathen man and a publican.
They had the church commission to preach the Gospel before Pentecost Mrk. 16:15 And he said unto them, Go ye into all the world, and preach the gospel to every creature.
Anyway, this part about the church before Pentecost is just a freebee. It doesn’t really speak to the issue of when the church was begun, but rather, when it wasn’t.