The Value of Common Prayer, by Abba Dorotheos (amateur translation)
I'll tell you something noteworthy that I heard from a great and clairvoyant Elder, that when he was in church, as soon as the brothers began to chant, he saw a brightly-clothed person come from the Holy Altar, holding a small circular vessel with holy water and an implement [μίλη] which he dipped it into the vessel and sprinkled [πέρναγε] all of the brothers, and signed them with the sign of the Cross. The seats that where empty, some he signed and others he sprinked without signing. And again, when the service was about to finish, I saw him exit from the Altar and do the same thing. One day, the Elder stopped him and fell to his feet entreating him to explain who he was and what was the meaning of what he was doing. And the brightly clothed person told him:
“I am an Angel of the Lord, and I received the command to sign all those who are found in the church from the start of the service and those who remain until its end, for their willingness and their dedication and their good intentions.”
And the Elder asked him: “And why do you sign the seats of some of those who were missing?”
The Angel replied: “Those of the brothers who are diligent with good intentions, but from some need or sickness however are absent with the blessing of the Fathers, or those who are obeying some command, and as a result they are somewhere completing this and are absent, all of these I sign, because though they are absent they are found with the others who are chanting. And only those who could be present but because of their negligence are absent, I have received the command to not sign them, because these alone have made themselves unworthy.
Let us take care, my brothers, to never lose the sign of the Holy Angel.
(amateur translation of Greek text from: http://voutsinasilias.blogspot.com/2010/04/blog-post_6969.html)