The Celtic year can be pictured as a wheel. Each season flows into the other and it's a cycle that continues on an on like a rolling wheel. In fact, some people think a Brigid's cross is the shape of a wheel and represents the four seasons. Imbolc (or Imbolg) is the day of the Feast of St. Brigid and originally belonged the Celtic goddess of the same name. Later the church used this festival and named it Candlemas, which is the blessing of the candles or more important to the church, the recognition of the purification of the Virgin Mary. From newadvent.org:
According to the Mosaic law a mother who had given birth to a man-child was considered unclean for seven days; moreover she was to remain three and thirty days "in the blood of her purification"; for a maid-child the time which excluded the mother from sanctuary was even doubled. When the time (forty or eighty days) was over the mother was to "bring to the temple a lamb for a holocaust and a young pigeon or turtle dove for sin"; if she was not able to offer a lamb, she was to take two turtle doves or two pigeons; the priest prayed for her and so she was cleansed. (Leviticus 12:2-8)But getting back to Imbolc, which is the Celtic festival, it's the beginning of spring, the time when new life was just beginning to reveal itself, the first planting of crops and the beginning of fishing season. It was also the day for hanging a new Brigid cross over the front door of your house or your barn. You can read more about the crosses in my post here.
It may not feel like spring where you live. It likely didn't in the land of these ancient people either. But it was the beginning, the hope of new life, fertile crops, young lambs and calves.