Bede, on Ps 137:1

“I will praise thee, O lord, with my whole heart: for thou hast heard the words of my mouth. I will sing praise to thee in the sight of his angels:”

“It is no secret that angels are frequently present, invisibly, at the side of the elect, in order to defend them from the snares of the cunning enemy and uphold them by the great gift of heavenly desire. The apostle attests to this when he says, "Are they not all ministering spirits sent to serve on account of those who receive an inheritance of salvation?" Nevertheless, we should believe that the angelic spirits are especially present to us when we give ourselves in a special way to divine services, that is, when we enter a church and open our ears to sacred reading, or give our attention to psalm singing, or apply ourselves to prayer or celebrate the solemnity of the mass. Hence the apostle advises women to have a veil over their heads in church on account of the angels. And a prophet says, "I will sing psalms to you in the sight of the angels." We are not permitted to doubt that where the mysteries of the Lord's body and blood are being enacted, a gathering of the citizens from on high is present—those who were keeping such careful watch at the tomb where [Christ's] venerable body had been placed and from which he had departed by rising. Hence we must strive meticulously my brothers, when we come into the church to pay the due service of divine praise or to perform the solemnity of the mass, to be always mindful of the angelic presence and to fulfill our heavenly duty with fear and fitting veneration, following the example of the women devoted to God who were afraid when the angels appeared to them at the tomb, and who, we are told, bowed their faces to the earth.”

Imported from an open dataset — not yet checked against the printed edition.