Really? Then why did Jesus say, "upon this rock I will build my church"? If the church has been established since Adam, he would have said "upon this rock I have built my church".
Not all Israel is Israel(Romans 9:6). Only a remnant of Israel was saved, eventhough the number of Israelites that came out from Egypt was in the millions. And even those who were born during their 40 years in the wilderness, only a remnant was saved. This remnant was the church in the wilderness(Acts 7:38).
Acts 7:31:38
31 When Moses saw it, he wondered at the sight: and as he drew near to behold it, the voice of the Lord came unto him,
32 Saying, I am the God of thy fathers, the God of Abraham, and the God of Isaac, and the God of Jacob. Then Moses trembled, and durst not behold.
33 Then said the Lord to him, Put off thy shoes from thy feet: for the place where thou standest is holy ground.
34 I have seen, I have seen the affliction of my people which is in Egypt, and I have heard their groaning, and am come down to deliver them. And now come, I will send thee into Egypt.
35 This Moses whom they refused, saying, Who made thee a ruler and a judge? the same did God send to be a ruler and a deliverer by the hand of the angel which appeared to him in the bush.
36 He brought them out, after that he had shewed wonders and signs in the land of Egypt, and in the Red sea, and in the wilderness forty years.
37 This is that Moses, which said unto the children of Israel, A prophet shall the Lord your God raise up unto you of your brethren, like unto me; him shall ye hear.
38 This is he,
that was in the church in the wilderness with the angel which spake to him in the mount Sina, and with our fathers: who received the lively oracles to give unto us:
Greek word used for church in Acts 7:38:
ekklēsia ἐκκλησία
G1577
1) a gathering of citizens called out from their homes into some public place, an assembly
a) an assembly of the people convened at the public place of the council for the purpose of deliberating
b)
the assembly of the Israelites
c) any gathering or throng of men assembled by chance, tumultuously
d) in a Christian sense
1)
an assembly of Christians gathered for worship in a religious meeting
2) a company of Christian, or of those who, hoping for eternal salvation through Jesus Christ, observe their own religious rites, hold their own religious meetings, and manage their own affairs, according to regulations prescribed for the body for order's sake
3) those who anywhere, in a city, village, constitute such a company and are united into one body
4) the whole body of Christians scattered throughout the earth
5)
the assembly of faithful Christians already dead and received into heaven
Jesus had the church in mind from the "get go". The "called out assembly" of Israelites constituted the church in the wilderness, just like the Church(again, a called out assembly) of today. In the OT, only a remnant was saved(the church in the wilderness), and in the NT, only a remnant is saved(the Church). Jesus' works on the cross brought this to fruition. He didn't go to the cross, and afterward set the church up. It was set up before He died and was risen, and He brought it to pass when He came forth from the grave and ascended back to the Father in the Cloud.