On the virtue that produces the rest
“Gratitude is not only the greatest of virtues, but the parent of all the others.”
Cicero said this in a courtroom, defending a man who had sheltered him in exile, so it is an argument with something at stake rather than a sentiment.
The claim is causal, and that is what makes it interesting. Not that gratitude is nice, but that the others come out of it — that someone who has genuinely registered what they were given finds generosity and loyalty already half-formed, and that someone who has not must manufacture them.