Funny, but I don't recall any requirement that one must be married. Paul never married, priests and nuns are banned from being married so just where do you get the idea that marriage is necessary? Paul did say that if you couldn't be like him then marriage is better than not marrying but nowhere is not being married listed as a "sin". Mariage at that time was expected because so many children never made it to adulthood and the parents needed someone- children- to care for them in their old age.