Translation:This gives a new meaning to that.
Le is necessary; a eso is reinforcement. But you really need both to be speaking Spanish, IMO.
I think "le" means "that" only because of the "a eso" at the end. Otherwise, it would just be "it" (or "him" in some cases based on context). Check out the site mannen listed if you haven't already done so -- it is helpful.
"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."
Thank you so much for that helpful answer it was one of the best explanation i had read so far on this discussion;-)
I just had 'This give a new significance to that' rejected - not sure why.