So can I parse the sentence as

'They, who honor in thee only what is best, honor thee best'

or, in plainer meaning,

'They [who] honor thee best [are thoese] who honor in thee only what is best'?

I’m learning English. If u find anywhere I can improve my composition, Pls do let me know. Bow.

Do inform me if you see any corrections needed in my written English.