The primary source that we develop our ethics from is the people we hang out with. We develop them because we tend to conform to the norms of the crowd that we are around. During studies, if everyone else gives the same wrong answer before the naive person answers, the naive person will also answer incorrectly the majority of the time (Shaw 22). In addition, those who go to the same church receive teachings from the same religion. Those teachings often tell people how they should worship and have social relationships (Shaw 11). As a result, those people tend to develop similar ethics based off of those teachings.
Shaw, William H. Business Ethics. 9th ed., Cengage Learning, 2017.