The one who treats you unfairly, tolerate him.
Firstly it is a quotation and quite famous, in fact so famous I cannot remember from where (red face) but I suspect it is biblical. Therefore it can and is written as seen.
Subject and Predicate Example:
In this example, “Ivan” is the subject and “jumped” is the verb. “Jumped” is the predicate of the sentence.
Ivan read a book to the students. In this example the meaning is Ivan, who read a book to the students.
In this example, the predicate of the sentence is “read a book to the students.” This is what Ivan does
The one (subject) who treats (verb) you unfairly, "treats you unfairly" is the predicate. This is what "the one does"
Ref "Writing Explained" What is a Predicate?