Who Is So Great A God As Our God?

A prokeimenon is a scripture verse that precedes a longer reading from the scipture.  Prokeimena come in a few different sizes. Most are fairly short, indeed the most common are just an intoned scripture verse before the epistle is read. In othros, the prokeimenon shows up right before the reading of the gospel reading (when there is a gospel reading). At liturgy, it shows up prior to the epistle reading. At vespers, it shows up after Gladsome Light. In common 'Byzantine' practice, the epistle prokeimenon is just intoned once with its verse. But all prokeimena were originally meant to be repeated after the verse is intoned. This is still commonly done in the slavic tradition, and occasionally it's still done in the psaltic tradition.

Sometimes the scripture reading that follows a prokeimenon gets misplaced (thus is vespers, which always has a prokeimenon chanted, but rarely has its old testament reading). Today's video is a vespers prokeimenon, but not one of the standard weekly prokeimena (like "The Lord is King, He is clothed with strength") but a festal vespers prokeimenon:

• This is a sticheraric piece in Grave Tone (aka Varys, sometimes called Tone 7). 
• There are different versions of Grave, this one is on the "enharmonic" scale on γα (more or less an F). That's why it sounds sweet.
• You sing this in the vespers for the day after Pascha, Thomas Sunday, Pentecost and Nativity.