Imbolc marks Winters end and Springs beggining. It is a time when women are honoured and represents the growth from the crone of Winter to the maiden of Spring.
Imbolc is sacred to the Goddess Brighid. (The Christians in an attempt to destroy paganism renamed this day Candlemas and took Brighid and transformed her into a Christian saint.)
It is also a festival of fire. Marking the return of the Sun. Hence the emphasis on candles.
The height of Spring. Cerrunos and the Green man are are both honoured here in order to ensure the birth of healthy offspring to all creatures...livestock, wild, and humans. And the fertility of the growing crops and the land.
It celebrates the return of greeness and life to the earth after the bleakness of winter.