An incantation is the collection of words that are recited as part of a spell or sometimes as the spell itself, such as a short rhyme spoken to make a wish at the sight of the first star of the evening. Incantations often take the form of chants and sometimes songs.
Many witches prefer to have their incantations rhyme. There is some advantage to this in that it makes the incantation easier to remember, particularly if it is one that will be used often, for calling the quarters for instance, but it is not necessary. It is also helpful for an incantation to have a rhythm as this seems to have a soothing and focusing effect, making the incantation more pleasant to repeat, focusing the mind to aid in reaching altered states of consciousness and helping to build energy. More important than either rhythm or rhyme, however, is the clarity of the incantation; incantations should be very clear and specific. While poetic language is acceptable, it is important that the incantation be difficult to misinterpret.
The purpose of an incantation during ritual, ceremony or spellwork is to make clear the purpose and direction of your working, to define your intent and send it out to the Universe and into your subconscious. An incantation may be used to praise, evoke or invoke a deity, to enchant an object or simply to focus the mind.