When it is said
The Orthodox burial service for a priest includes the whole psalm, which ends with these four verses.
Anyone growing older can pray them as a promise, or read them over someone whose long life has borne fruit.
Where it comes from
No author known
A psalm for the Sabbath
The Hebrew heading calls it “A Psalm, a Song. For the sabbath day,” and names no author. St Athanasius of Alexandria wrote a letter to Marcellinus on how to pray the Psalms. When he comes to the Sabbath, he gives this psalm as the one to sing that day.
The Hebrew with the Jewish Publication Society’s English (Mechon Mamre); St Athanasius, Letter to Marcellinus on the Psalms, in the Greek (Documenta Catholica Omnia)
Old age in the Greek
The Septuagint (the ancient Greek translation of the Hebrew Scriptures) numbers it Psalm 91, and it speaks of old age twice. Where the Hebrew says the righteous will still bear fruit, the Greek says they “shall be increased in a fine old age.” A few verses earlier, where the Hebrew speaks of fresh oil, the Greek reads “mine old age with rich mercy.”
The Scripture in it
The righteous will flourish like a palm tree, and grow like a cedar in Lebanon. Planted in the house of the LORD, they will flourish in the courts of our God. In old age they will still bear fruit; healthy and green they will remain, to proclaim, “The LORD is upright; He is my Rock, and in Him there is no unrighteousness.”
Bible text: Berean Standard Bible, public domain.