St. Augustine interprets Psalm 123 as if it is the song of martyrs who have escaped their torments.
The exultant members of Christ are singing this Psalm. But here below who sings exultantly except in hope? But because that hope of ours is certain, we too sing exultingly. Those who are singing are not strangers to us, and it’s not as if we do not find our voice in this Psalm. Listen to it as if you were hearing yourselves. Listen to it as if you were seeing yourselves in the mirror of the Scriptures. When you look at the Scriptures as if in a mirror, your face rejoices when you find yourself in your exultant hope like those members of Christ who are singing this song. You, too, will be among those members, and you will sing this song. [In Ps 123,3; PL 37:1641]