The first assembly of the called out was the household of Abraham, who all left country, kindred and home to cross over at the call of the LORD. Apostasy from that community led Lot to turn his face toward Sodom.
The same turning away was evident within forty days of the children of Israel promising "All that the LORD has spoken we will do, and we will be obedient." (Exodus 24:7) The Golden Calf incident nearly led to the total obliteration of this particular disobedient ekklesia or "son" which had been called out of Egypt. Only Moses and Joshua would have been spared.
Joshua's renewal of protection (Joshua 1:5) was as contingent upon his effort toward obedience as that of the children at Mt. Horeb:
"Only be strong and very courageous, being careful to do according to all the law that Moses my servant commanded you. Do not turn from it to the right hand or to the left, that you may have good success wherever you go. This Book of the Law shall not depart from your mouth, but you shall meditate on it day and night, so that you may be careful to do according to all that is written in it. For then you will make your way prosperous, and then you will have good success. (Joshua 1:8,9)"
Skipping ahead to the contemporary assembly that Jesus called out, the apostatic process was evident to Jude who reminded his readers that if the wayward children in the wilderness were not spared, why should their fate following disobedience be different?
The process of turning away is not a singular event in history, rather it is a consequence of the human "sin nature".
The question is from what did those in ancient days turn?