Translation:This gives a new meaning to that.
"Le" is used because it's an indirect object (IO) not a direct object (DO). "Lo, la, los, las, nos, te, and me" are all DO pronouns.
The DO is the object acted upon by the verb. In this case the verb is "give," so the DO will tell us what was given. In this sentence the thing given was "a new meaning."
The IO is the object which received the DO. In our case we're only told the "new meaning" was given to "that." Since we're not told what "that" is, we are required to use the IO pronoun "le."