Lazerlike42
Darth Incompetant
It wasn't a big change. The correct day of worship was Sunday, but most people did not follow it. It wsa very difficult to overcome old habits and beliefs. Even the gentiles, who had not had old Jewish beliefs, fell into old Jewish practices because:
A) they knew Jesus was of the Jews, and knew how the Jews behaved and tried to mimic them
B) many gentiles were instructed to continue in old Jewish practices by Jewish converts who themselves had not abandoned these ideas yet
C) many gentiles were shunned by the Jewish Christians if they did not practice the old ways
D) Christianity was an illegal religion in the Roman empire, and many people simply had to practice in the old ways, especially in such obvious ways as to gather on Saturday, to avoid being caught.
E) People misunderstood the concept that was taught in Romans 14 (though people at the time learned this concept mostly from Paul's missions as opposed to this epistle which fewer actually had read to them or saw)
In fact, much of the book of Hebrews addresses this. Paul himself spends a lot of time addressing this type (though not this specific) problem. He even had to correct Peter (2 Galatians) because Peter was afraid of confronting the Jewish Christians about their old practices so he began to do them himself.