Sirach 6:16
Ben Sira, Ecclesiasticus14 Faithful friends are a sturdy shelter: whoever finds one has found a treasure. 15 Faithful friends are beyond price; no amount can balance their worth. 16 Faithful friends are a bag of life*; and those who fear the Lord will find them. 17 Those who fear the Lord direct their friendship aright, for as they are, so are their neighbors also. 18 My child, from your youth choose discipline, and when you have gray hair you will still find wisdom.
Ambrose On the Duty of the Clergy 2.7
37 It gives a very great impetus to mutual love if one shows love in return to those who love us and proves that one does not love them less than oneself is loved, especially if one shows it by the proofs that a faithful friendship gives. What is so likely to win favour as gratitude? What more natural than to love one who loves us? What so implanted and so impressed on men's feelings as the wish to let another, by whom we want to be loved, know that we love him? Well does the wise man say: Lose your money for your brother and your friend. And again: I will not be ashamed to defend a friend, neither will I hide myself from him. If, indeed, the words in Ecclesiasticus testify that the medicine of life and immortality is in a friend; yet none has ever doubted that it is in love that our best defense lies. As the Apostle says: It bears all things, believes all things, hopes all things, endures all things; love never fails.
Notes and References
"... As a second example of reception history, we can consider another oft- cited Sirach passage, the first poem on friendship (Sirach 6:5–17). Within Jewish tradition, the Babylonian Talmud cites a form of the admonition in Sirach 6:6: “Let those who seek your peace be many; reveal your confidence to one in a thousand” (b. Sanhedrin 100b). Several references to Sirach 6:5–17 occur within Christian literature from the late fourth century. Testimony to the friendship existing among the Cappadocian Fathers is evident in the oration, pronounced in 372 by Gregory of Nazianzus (d. 389), shortly after he was made bishop, in the presence of his two friends, Gregory of Nyssa and his brother Basil of Caesarea. Acknowledging the value of their friendship, the oration refers to Sirach 6:14–15 (Or. 11). Around the same time, Ambrose of Milan (d. 397), twice quotes Sirach 6:16, in association with other verses of Sirach on friendship, in its expanded Latin form: “A faithful friend is a medicine of life and immortality” (Off. 2:7 [37]). Another contemporary bishop, John Chrysostom (d. 407), refers to Sirach 6:14–16 to explain the extent of true friendship (Hom. 1 Thess.), while commenting on Paul’s tender treatment of his converts in Thessalonica (1 Thessalonians 2:7–8) ..."
Corley, Jeremy "Sirach" in Oegema, Gerbern S. (ed.) The Oxford Handbook of the Apocrypha (pp. 284-305) Oxford University Press, 2021