This is the second of the five faithful sayings. The other four are all translated with that word, ‘faithful’, but our translators chose to use a different word in 1 Timothy 3.
There is of course a personal call to office, to the ministry in particular, but there is also the need for this to be confirmed by the church and that is implied here. We read in the Scripture of there being a personal and inner call, but that is not all there is to it, because it is the church that is to discern whether that person is truly called; it is the people of God who are to corroborate that call. That's why these instructions are being given. Timothy here is a presiding elder or pastor, and he is to see to it that the apostle’s rules are kept. Certain standards must be met: the person must be proved; the person must have functioned in some limited way in a similar area and acquitted himself well.
Some people romantically imagine they are called to missionary service, and off they go to a college and the church really hasn't sanctioned it at all. The church really hasn't said, this person has obviously been equipped by the Lord, and has proved it in all his service, in all that he's done.
How many elders does a church need? In our own tradition here, when Spurgeon had more than 4000 church members, he had 20 elders. That is one per 200 church members. Nowadays you can find churches as small as 60 or 70 people with 7, 8, 9 elders and that seems too many. Eldership is not a badge of hour; it is an office with a practical purpose.