Albert Barnes Commentary Psalms 79:11

"Let the sighing of the prisoner come before thee: According to the greatness of thy power preserve thou those that are appointed to death;" — Psalms 79:11 (ASV)

Let the sighing of the prisoner come before you — This refers to the sighing of the one who is bound. The allusion here is undoubtedly to those among the Hebrews who had been taken captive and who sighed not only because of the sufferings they endured in their bondage, but also because they had been taken from their country and home. The meaning is: Hear those sighs, and come for the deliverance of those who are thus held in captivity.

According to the greatness of your power — The margin, as in Hebrew, reads "your arm." The arm is the symbol of power. It is implied here that great power was necessary to deliver those who were held in captivity—power such as God alone could exert, power which could be wielded only by an Omnipotent Being. It was the power of God alone which could rescue them, just as it is only by the power of God that sinners can be saved.

Preserve you those that are appointed to die — The margin reads, "Reserve the children of death." The literal meaning is, “Let remain the sons of death;” that is, preserve those who are in such circumstances that death is impending, and who may be called the sons of death. This might apply to those who were condemned to death, to those who were sick and in danger of death, or to those who were prisoners and captives and who were, by their sufferings, exposed to death. The prayer is that such might be allowed to remain on the earth; that is, that they might be kept alive.