OSBERT de CLARE. - English Benedictine theologian of the 12th century, born at Clare (county of Suffolk). He became a monk of Westminster Abbey and, c. 1136, its prior. He was a learned and able champion of the doctrine of the Immaculate Conception of Mary and promoted the institution of the feast, which was strongly opposed by Roger, bishop of Salisbury, and Bernard, bishop of St. David’s, and many others, although the feast was observed in England before the Norman Conquest (1066).
The Council of London in 1129 decided in favor of the feast, and Gilbert, bishop of London, adopted it in his diocese. Osbert was a friend of Anselm (nephew of the saint), abbot of Bury St. Edmunds. He was sent to Rome c. 1141 by King Stephen (1135–54) with his abbot to petition the Pope for the canonization of King Edward the Confessor. Osbert deserves great honor for his *Epistolae* to Anselm and to Warin, dean of Worcester, and for the sermon *De Conceptione Sanctae Mariae*, in which he set forth clearly and ably the theology of the Immaculate Conception. He also wrote the lives of SS. Edward, Edmund, and others. He has sometimes been confused with the hagiographer Osbern (who flourished c. 1090).