Elders and Deacons
Elders and Deacons are like Aaron and his sons. The numbers explain.
1 Timothy 3:1-10
Count
1+2 = 3 = Leviticus
Leviticus
Aaron and his sons were ordained to serve as priests before Yahvah on behalf of the assembly of Israel. This is the model behind the role of Elders and Deacons, which serve in various assemblies of god in a similar way, the major difference being they are appointed or ordained upon passing examination and not by force of inheritance as sons of Aaron.
This is profound because it says Elders are like the high priest and stay around in one place while Deacons are like the under priests or even the levites who assist the high priest and help as the "step and fetch it" or messenger between different assemblies.
Thus the Elders have a primary role in helping Deacons grow and Deacons are the pool from which new Elders are appointed.
Functionally Deacons probably travel between assemblies delivering communication or financial aid and what not. In so doing the hosting Elders would be able to examine. Those with a good reputation with outsiders and passing examination over some period of time serving in this capacity would be worthy candidates for appointment to the role of Elder within a specific (one wife) assembly, thus switching to the facilitating, hosting, teaching function in one place and letting others travel around as Deacons.
Like with any family it would be the case that sons eventually grow up and leave home and start families of their own. It may be that a spiritual son serving an Elder would need to go to start a new assembly when he moves to the role of Elder himself.