Circles of concentration are basically levels of engagement that a ritualist must understand in order to do effective group ritual.
The first circle of concentration is the self: understanding and knowing what you are doing at any given time, as well as being aware of "the critic" who sits at the back of your mind and ensures that you don't fall into a hole while you're trying to open the Gates. This circle is about you, your connection with the deities, and staying on your feet.
The second circle of concentration encompasses the other participants in the ritual: each person who is doing ritual with you is accounted for and you are aware of what they are doing. If you are maintaining this circle as well as the first circle, than you have all the liturgists/ritualists accounted for in your mind, and you are connected to them in such a way that you won't bump into them. . . and more importantly, you are aware of them and their first circle connections: if something starts to go wrong or if one of you needs to get the attention of the others, it is easier because you are all aware of the others.
The third circle of concentration is the awareness of and connection with all those members of the congregation who are not actively participating in the ritual. This ensures that the experience of the liturgist/ritualist is available to the attendee, and vice versa. Without this circle, a liturgist could find themselves so focused on doing the ritual that they do not fully experience the sense of wonder and joy that a ritual is meant to engender.
By maintaining all these circles, the ritualist can connect with everyone, perform ritual at a higher level, and not step in a hole and break an ankle.
- Thomas, Kirk. "Circles of Concentration in Ritual." 2007 Trillium Festival. Log Cabin Campground, VA.