Painting of The Vigil , 1884. Oil on canvas by English artist , John Pettie. During the Middle Ages , a squire on the night before his knighting ceremony was expected to take a cleansing bath , fast , make confession , and then hold an all - night vigil of prayer in the chapel , preparing himself in this manner for life as a knight . For the knighting ceremony , he dressed in white as a symbol for purity .