Roman Catholic, Anglo Catholic and Orthodox people address their cleric leaders with titles which seem to be unscriptural, i.e., "My Lord," "Most Rev. Father," etc. Where did these titles originate, since the apostles never used such titles for themselves?
The origin of clerical titles is, as you might imagine, rather complex and varied. Many developed after the time of the Reformation, apparently, such as addressing a parish priest as "father." The more elaborate titles for higher clergy were in imitation of such being used for nobility and royalty, as was so much in the development of ecclesiastical government over the course of years. The reasoning was that if such exalted forms of address could be used for those who held secular titles, how much more so for those who held ecclesiastical ones. This tends, of course, to obscure the teaching of our Lord concerning the character of kingdom service and the meaning of servant leadership (cf. Matt. 23:5-12; Mark 10:35-45; John 13:1-20). I trust that this proves useful to you.