In Gerald Ford's eulogy, Henry Kissinger said:
According to an ancient tradition, God preserves humanity despite its many transgressions because, at any one period, there exist ten just individuals who redeem mankind, without being aware of their role.
Which is this ancient tradition and is there any context why this particular reference was chosen to praise the dead president?
The reference is to Genesis chapter 18. God and Abraham are having a conversation about Sodom and Gomorrah, and whether God will destroy the cities. God tells Abraham he is going to destroy the cities, and Abraham asks if God would spare the cities if he could find 50 good men. God says sure. So Abraham's like shit I can't find 50 and eventually bargains God down to ten. So if Abraham could find ten good men, God would spare the cities. The quote no doubt references that Ford was one of the ten good men that could be counted in order to save the cities aka man kind.
Ninja edit: Ford was an Episcopalian and noted the role of his religion in his life in some of his reflection papers. The link includes a photo of those reflections.
https://www.fordlibrarymuseum.gov/library/document/0065/atth-religion.pdf