What was the most important achievement of the pope Gregory 1?

Pope Gregory I, also known as Gregory the Great, is best known for his role in the development of the medieval papacy and the consolidation of papal authority. His most significant achievement was the establishment of the Gregorian Chant, which greatly influenced Western music and liturgy. Additionally, he played a pivotal role in the spread of Christianity through missions, notably sending Augustine of Canterbury to convert the Anglo-Saxons. Gregory's writings and reforms also helped to shape the Church's administration and its relationship with secular rulers.