The Ember Days give us clues, I think, to dimensions of the Church's liturgy which go back to ancient Church usage. They are a little like the liturgy of Holy Week in that way. So, for example, we have this week, on Ember Wednesday, Ember Friday, and Ember Saturday, some of the very few occasions in the Church Year when Old Testament lessons are called for at Mass.
Another unusual phenomenon is the following rubrical rarity. Before the collect, the celebrant says, "Oremus." The Deacon then says, "Flectamus genua." Then the subdeacon says, "Levate." (When the priest celebrates low Mass, he makes all three announcements.) Fr. Petersen poses the question at his blog as to why this does not take place in the Ember Friday Mass. It's a good question. I'd like to research it myself when I am able. And if any reader of this blog has the answer, please share it.
A couple of comments are worth making on this rubric. It is designed to give the people a distinct, prolonged moment in which to silently pray, before the "Levate" (which is perhaps best translated "Arise") is announced. Therefore the flectamus genua is a call to kneel, that is, to lower to both knees. Even though we often, and understandably, translate flectamus genua as "genuflect," in this case I would argue we should translate it as "Let us kneel." For a genuflection is a lowering the right knee to the floor, and for just a moment, then returning right away to standing position.
The concept behind this rubric, I think, is that we are called upon to silently bring before God our petitions, and then for the Church's yearnings and prayers to be "collected" in the collect.