There are three categories of elder referred to in this verse. A superficial look might conclude there are only two categories of elder.
There is so little conviction around today, even among the ranks of pastors and ministers. Sometimes pastors seem to hold the truth of God more as you hold an opinion than a deep conviction. Paul has warned that some will depart from the faith. This is always the way. Satan's chief wiles are to flood the true church of Christ with false notions, which tear away at the faith of believers and their walk and commitment. It is common today. How is it that Britain lost its major Protestant denominations so that today, in the Church of England, only a fraction of the parishes will have a Bible-believing preacher? How is it that in the great company of Methodists – when you think of all that Methodism stood for – today, you would have to hunt high and low for a Methodist chapel where the truth was taught? Shocking things are enacted, put into practice by the Methodist Church authorities. How did all that happen? How did whole denominations lose the gospel? The Baptist Union of Great Britain and Northern Ireland, 150 years ago, was always entirely evangelistic and mainly Calvinistic. It's all gone. Most Union churches now are doctrinally deeply corrupt and have no gospel light. There's just a small number of people left. Congregationalists, almost none, completely taken over by theological liberalism. How did we lose such a heritage? The elders, the deacons, the people took things lightly.
Why does the apostle use two quite different terms for similar service? In chapter 3 and verse 1 he uses the word bishop, and he says, ‘This is a true saying, If a man desire the office of a bishop’ – that is an overseer in the original, a watcher. Then in chapter 5 and verse 17, he calls the same person an elder. Why use two terms, when one will do? Because the term overseer, the person who watches out, that describes the function of the elder. Whereas the term elder tends to describe his status or his office, or maybe even hints at his qualifications. If not necessarily an old man in years, he will certainly not be a newcomer to the faith. He will be someone of some experience in the things of God. The term elder suggests that he is a senior person in the church and therefore he is to be prayed for, to be respected for his work's sake. Of course respect is to be earned. We've seen that in a previous chapter. It isn't automatic.