During spell work and some magico-religious rituals, a Circle is cast to define the sacred ritual or work space and separate it from its mundane surroundings. This Circle is a construct of energy and it is designed to contain energy within it. Beyond that, the purpose of the Circle can vary by tradition.
Casting a Circle for Spellwork
During spellwork, the Circle creates a sort of storage unit for the energy of the spell. During the creation of the Circle, any energy not associated with the spell is banished from the area and the Circle creates a sort of barrier containing the energy raised by the practitioner and preventing outside energy from entering and affecting the energy within.
It is important during spellwork that no one leave or enter the Circle because the moment you step out of the sacred space, your energy begins to normalize and it is affected by everything you see and touch and any sounds you hear so that when you return to the charged Circle, the charge will be affected by the energy you bring in and may lose potency. Your focus will be off and the atmosphere of the Circle will be affected. Not the end of the world, but not conducive to effective magick either.
Casting a Circle for Ritual and Worship
Circles are often cast for ritual purposes unrelated to specific spellwork such as those to honor deity or to mark festival days such as those found on the Wheel of the Year. While this Circle also contains the energy raised during the ritual, this energy is less intentional and more organic. You are there to celebrate, the energy just happens. The purpose of the Circle in this case is primarily to establish the sacred ritual space and create a boarder between it and the mundane world. This is especially important where ritual space must also be used for mundane purposes during mundane occasions, such as living rooms and kitchens.
Leaving this circle might alter the mood, and probably shouldn’t be done if a deity is present out of decorum, but during a festival, a general festive mood should be everywhere and I don’t think crossing a circle in this case does any harm. Some people disagree.
A Circle of Protection
Many will disagree with the above reasoning for casting a circle for spellwork and ritual as many consider the Circle to be a protective barrier. In this case the purpose of the Circle is to keep out unwanted entities that would feed off the energy being raised or use the opportunity presented by your focus on something else to attach itself to you. Not everyone believes this to be an issue, though many do. It is thought by those who do that using magic can draw the attention of spirit beings and not all of them are friendly and helpful.
There is no reason both scenerios can’t be true. The Circle is an energetic barrier and spirit beings are beings of energy.
Whether you cast a Circle of Protection every time you cast a spell or perform a ritual or not, it can also be cast simply for protection without creating sacred space within at all. Some cast a Circle around themselves when feeling threatened, or around their children, their homes, their valuables. It is handy to practice casting on a regular basis, so that you can cast it quickly when the need arises. This can also be done while dreaming and astral projecting. The only difference between this kind of a circle and another is intention.
Crossing a protective Circle is not advised. If you can cross it, why not anybody?
In some Ceremonial Magick practices, the Circle may be used to contain an entity that has been summoned into it against its will. The practitioner stands outside the Circle in this case and the entity is invoked into the Circle. The energy barrier of the Circle prevents the entity from exiting, thus protecting the practitioner and the general neighborhood.
The Process of Casting a Circle
A circle is generally cast by “drawing” a circle with energy. The Circle may also be physically drawn using paint or chalk or marked out with candles or scratched in the dirt, but this is not necessary. The energy to create the Circle may be drawn up through the practitioner and directed out from the finger or a tool like a wand or athame and sent to the perimeter of the circle, often visualized as a glowing white ring of flame or just glowing energy- usually white in color. It is extremely important that the energy being channeled for the Circle be charged with the appropriate intention. If it is a Circle for protection, the energy should be charged for protection, for containment, likewise. Words are often spoken, chanted or intoned to aid this process.
In group situations, the energy may be passed from hand to hand with the practioners’ bodies forming the circle.
Opening the Circle
Once you have completed your work within the Circle, any residual energy (or entity) contained within is banished (Or released, if you prefer) and the Circle is opened or destroyed. The energetic barrier is removed and the space is returned to normalcy. The simplest way people do this is to simply declare the Circle open. Some go through the steps of re-absorbing the energy, performing the actions used to create the Circle in the first place in reverse, visualizing the energy fading from the Circle and/or returning to the hand, wand or athame from whence it emerged. Some just visualize it flickering and fading.