They must keep hold of the deep truths of the faith
with a clear conscience."
1 Timothy 3.9
When it comes to the role of the deacon, there is one verse which speaks of the partnership in the gospel between the overseer/elder and the deacon and that is v.9
The Deacon's responsibility
There is no suggestion that deacons have a teaching function, though there is nothing to say that they couldn't. What is clear, though, is that teaching is not core to being a deacon. You can see why. Distributing funds to widows, doesn't require teaching, organising the team to set up the room for worship doesn't require teaching, providing food for the meal doesn't require teaching.
However, Paul says that they should keep hold of the deep truths of the faith - that that is a key part of their responsibility. This is so that this group of leaders will provide a doctrinal centre of mass for the people of God - a ballast of truth - a gospel inertia. Inertia is normally seen as a bad thing in our society - change is always good. In certain areas of the church's life, that is true, but not when it comes to doctrine. It's why we still say the ancient creeds in our church.
The other day I was watching Deepwater Horizon. It's a good film, although it is clearly a sign of my age that I wish that they would enunciate their words more clearly! The film is centred around a floating oil rig. It is not fixed to the ocean bed, but keeps in position over the same spot by the use of propellers under the surface of the water. This means that when waves hit the rig, or the wind blows, the rig holds its position.
Deacons are like those propellers - they hold onto the teaching from godly overseers, so that the church as a whole keeps its position over the gospel. They will also as a result recognise false teachers/overseers and resist being moved by them (cf. 1 Tim 1.19-20).