So, I saw this video
, along with some others, of Metropolitan Jonah serving just a few weeks ago. In these videos, as you can see, he's vested just like a priest, except that he wore the small omophor, the panagia and the Christ engolpion. He also carried a crozier.
What exactly is the reasoning behind this? Was he serving as a priest? I've only seen a bishop serve as a priest once, but he still wore his full episcopal vestments. I'd be interested to hear from folks that know a lot more about this than me...
This is not unheard of. My own bishop has been known to do this.
When there are not enough subdeacons, servers, and choristers (or at least not enough who know how to serve the hierarchical services, as often happens when bishops visit small missions in their dioceses which do not have many resources or much experience of the services), a bishop will sometimes forgo the hierarchical services and vest more simply. He may choose to use the trikiri and dikiri or he may not, and the same goes for the omophor. I think that the reasoning is that it is better to offer God a simple service done well and with dignity than it is to make a shambles of an elaborate service. The basic principle: "We should do the best we can with what we have".
Anciently, the phelon in the east or the chasuble in the west (which are the same vestment in origin) was worn by bishops as well as priests. The sakkos as the distinctive vestment of Byzantine-rite bishops only came later.(I hope you'll forgive a spot of Sunday evening pedantry. "Alternate" means something used in turn or rotation with something else, such as wearing red socks on a Monday, blue on Tuesday, red on Wednesday, blue on Thursday, and so forth. Something done instead of something else is an alternative, not alternate.)