The season pass normally goes for $20 (or thereabouts) but is currently part of Origin's On the House program, meaning that it's yours if you want it at the low price of zero. Obviously you'll need to own Star Wars Battlefront to play it, but EA will give it to you, along with a notice that you won't be able to actually do anything with it, even if you don't.
The Star Wars Battlefront season pass includes four expansions—Outer Rim, Bespin, Death Star, and Rogue One: Scarif—that collectively add four new game modes, eight heroes (and/or villains, depending on the firmness of your commitment to the principles of law and order) and 16 maps. There's also a "Shoot First" emote, which is presumably an animated image of George Lucas laughing while holding two canvas sacks emblazoned with large dollar signs up over his head.
The one knock against On the House is that, as far as I know, EA doesn't give any indication as to when an On the House offer will end, so I'd suggest getting it while the getting is good. And if you don't own Star Wars Battlefront, you can either pick it up for a fiver or get it as part of the Origin Access subscription program.