1 grave robbers,mistaken about which cave,possibly agreed upon to meet at that place prior to the crucifixion. 2 it is believed back then the only ones to know it was in fact jesus would be his apostles/family/close friends any of the 500 he supposedly came back to see may never have met him before and could have actually just spoken with a stranger or apostle sent with a message by Jesus to go and speak to these ppl. Also given the time period this could be claimed with no evidence no one would argue it happened as nobody could prove it didn't. 3 the church grew and has continued to due to human fallibility.many are taught from very you cementing in their minds that it is true if i raised my children with such fervour claiming there's a pink unicorn in the sky they would grow up believing it to be true humans are very easily taught to accept things a true especially when taught from a young age. Also jesus was against organised religion so the church while perhaps sending out his message is doing it in the incorrect way.