On the night of July 26th 1620, the feast day of St. Anne (according to tradition the mother of the Virgin Mary) Anne appeared to a nun and told her that it would be pleasing to Heaven if the statue was crowned. Since the Madonna of Oropa has worked so many miracles and has become so important to the Italians, she was crowned not only by the Pope of that year, but by three other Popes, once every hundred years, in 1620, 1720, 1820, and 1920. Hence the 3 crowns and the halo with diamond studded stars.(*1) Like many Black Madonnas, Our Lady of Oropa was invoked against the Black Death, the bubonic plague.
The statue captures a scene described in Luke 2:22-24 as the ceremony of purification (of Mary) and the presentation and dedication of Baby Jesus to God. These were performed in accordance with Mosaic law forty days after the birth of Jesus. Mary holds in her right hand the coins for the temple offering and Jesus in his left the sacrificial dove.
Until recent times the commemoration of this event was a major feast day celebrated in February with processions and the blessing of candles. Hence its name: Candlemas. When Christianity was introduced into Europe this feast day was used to supplant several pre-Christian celebrations. There was the Roman holiday called Lupercalia, which marked the end of the old year (in February) as a time of purification. February comes from Latin februare, which means to purify. It was a time to chase away any evil of the old year and to invoke the fertility of the new. Other Europeans celebrated "Imbolc" as the first stirrings of Spring in Winter.
Under Catholicism, the Virgin Mary came to represent all of creation being purified and the light of Baby Jesus' presentation to God became the spring of a new era.
*1: For more information see: Franciscan Friars of the Immaculate, "Marian Shrines of Italy", Park Press: Waite Park, MN: 2000, pp.82-6