Christian authorities in Europe and the Near East spent a great deal of the first millennium legislating dance out of worship, and largely succeeded. The Ethiopian church did the opposite. Aquaquam is not a survival tolerated at the edges of the liturgy, it is a clerical office with a curriculum, a technique and examinations, performed at the centre of the greatest feasts by the most highly trained people in the building.
The justification the tradition gives is scriptural and it is offered without embarrassment: David danced before the ark. Where other churches read that passage as belonging to an earlier dispensation, Ethiopian practice reads it as a warrant. The connection is made concrete in the liturgy, because the tabot, the consecrated altar tablet that represents the ark, is what the clergy process with and dance before on the great feasts, most visibly at Timkat.
The movement itself is restrained. Two rows of debtera face one another, holding the prayer staff upright, and move with a slow stepping and a swaying of the upper body, accelerating gradually across a long performance. The sistrum is shaken on the beat and the kebero drum underneath it carries the pattern. Nothing about it is improvised or ecstatic. A visitor expecting something loose finds a discipline closer to a drill, performed by men who have spent years learning the chant it belongs to before being allowed to move to it at all.