"the best of friends" vs "best friends" from quora.com:
"they are the best of friends" usually means two people who get along very well despite being very different. Quite often a little kid of speaking age who forms an attachment to an adult they see fairly frequently such as the postman and always likes to see him for a little chat. Family members will say "oh yes, they are the best of friends".
Whereas when we recognize any two people usually of the same gender, who have a lot in common and maintain a close friendship, from school kids through to oldies, we readily say "they are best friends"
"They are the best of friends" means they are good friends. They get along well together. It can apply to a small group of people who hang out together.
"They are best friends" refers to two people who truly rely on each other and without one the other would feel lost.
I understand what "best friends" means.
I understand why "best friends" means what it means.
I understood from the text above what "the best of friends" means.
But I don't understand why "the best of friends" means what it means. That is, from where does it take such a meaning?
They are the best of friends. — I can only understand it as "They are the best of those people who we consider as friends", but the meaning explained above is different. How did "the best" and "friends" connecting with "of" begin to mean something other than the usual phrases having "of", e.g. "one of my friends teaches yoga" ?
Maybe "of" in "the best of friends" has some special meaning - in this case, could you please show me it in a dictionary?