I think the first thing we need to realize is that historically there was no such distinction in the church and in the English language. Simply look up joy in a secular dictionary, say Webster’s Dictionary, and you’ll see it defined as happiness and, happiness defined as joy. They are synonyms with overlapping meanings. 

There’s a long rich, history of equating joy with happiness in Christ. In stark contrast to believers prior to the twentieth century, many modern Christians have portrayed happiness as, at best, inferior to joy and, at worst, evil.