Esbats, or Lunar Sabbats, occur every month on the full moon. Not every tradition incorporates Esbats as a part of their monthly rituals, and some prefer to use other phases than the full moon for special rites. But in general, Esbats help us to reflect on the events of the month, where we are, and where we need to go in our lives in the months to come. It is a time of reflection, evaluation, thought, and joy about what may happen (or needs to happen) before the next full moon. Just as the moon affect the tides, many people believe the moon affects the flow of forces in our lives, and therefore should be an important ritual focal point. By celebrating the natural monthly and yearly ycles through ritual, we can attune ourselves to nature and the Divine that is inherent in all things.
The Celts, according to what little we know, celebrated 4 major festivals during the year, known as Fire Festivals. They are associated with both the seasons and tied to the phases of the Moon. The Celtic fire festivals, in a tradition that many pagans hold, are celebrated from dusk of the day before to dusk of the designated Sabbat, and most of the festivities occur at night, the main ritual being held during the Full Moon. They are primarily directed at forces involved with agriculture, nature, pasturing and livestock. Most Celtic festivals also focus around the traditions of the people, and the ancestors who gave them their traditions.
The Celtic year is divided into halves, marked by the two great Fire Festivals of Samhain and Bealtinne. The period from Samhain to Bealtinne is called (in Irish Gaelic) "an Ghrian beag" or the "lessor Sun", and this makes since as during that time period it is cooler and the days are shorter. The period from Bealtaine to Samhain is called "an Ghrian mor" or the "greater Sun". The days are warmer and longer. The Celtic year is further subdivided by the other two yearly fire festivals, Imbolc and Lughnassadh.