This Sunday is of course the feast of the Dedication of St Michael, that is of the Church of Monte Sant'Angelo sul Gargano in Italy.
The feast of St Michael has been celebrated on this date since the fifth century following a series of apparitions of St Michael the Archangel in 490 to the Bishop of Sipontum near a cave, asking that the cave be dedicated to Christian worship and promising protection of the nearby town of Sipontum from pagan invaders. Pope Gelasius I (reigned 492-496) directed that a basilica be erected enclosing the space.
The texts of the feast, though, are not those of the dedication of a Church, but rather go the interventions in history of St Michael himself, as well as the angels more generally. The Office of course, includes commemorations of the Sunday at I Vespers as well as on the day itself, and these are for the fifth Sunday of September, and the Nineteenth Sunday after Pentecost.
There are a number of other important feasts this week in the traditional Benedictine Office, as you can see from the summary:
Sun 29 Sept Dedication of St Michael the Archangel, Class I
Mon 30 Sept St Jerome, Class III
Tues 1 Oct Class IV
Wed 2 Oct The Holy Guardian Angels, Class III
Thurs 3 Oct St Teresa of the Child Jesus, Memorial
Fri 4 Oct St Francis, Class III
Sat 5 Oct SS Maurus and Placid, Class III