The last thing said before sleep, and it is nearly the same every night on purpose. You are not meant to be alert for this one. About eight minutes, and it ends with a prayer for a peaceful death that people have said nightly, without drama, for fifteen hundred years.
A minute, in silence. Not an inventory — just where the day went, and where you went with it.
ThenO my God, I am heartily sorry for having offended thee, and I detest all my sins because of thy just punishments, but most of all because they offend thee, my God, who art all good and deserving of all my love. I firmly resolve, with the help of thy grace, to sin no more and to avoid the near occasions of sin. Amen.
And thenGlory be to the Father, and to the Son, and to the Holy Spirit. As it was in the beginning, is now, and ever shall be, world without end. Amen.
TraditionalMay the almighty and merciful Lord grant us a quiet night and a perfect end. Amen.
It is the same every night, and that is the feature. You are tired, and the hour asks nothing of your concentration — it hands you words you already know so you can say them badly and still have said them.
It looks back briefly, admits what there is to admit, and then stops looking back. That is a real thing to be given at the end of a bad day: a place to put it and a point where you are done handling it.
And then it says something strange, every single night. The Nunc Dimittis is an old man's prayer at the end of his life — now thou dost dismiss thy servant, O Lord, in peace — and the Church puts it in your mouth before every ordinary sleep. Going to bed rehearses dying, quietly, and the hour treats that as nothing to be frightened of.
Benedict, around the year 530. His Rule sets out the hours of the day and ends with this one, and he is specific about it: it is said last, after which nobody speaks, and it is the same every night so it can be said from memory in the dark. That instruction is why the hour has the character it has.
It spread with the monasteries and then out of them. By the late Middle Ages Compline was in the Books of Hours that laypeople owned — often the one hour an ordinary literate household actually kept — and the Marian antiphon at the end of it is where the Salve Regina lives.
If you wake later and cannot get back to sleep, that hour has its own prayer too: the middle of the night.