Barcelona will have to use all best players they have for this El Clásico. Win it and keep up their hope and chance to catch Real Madrid with 5 points when season will have 6 more matches after this El Clásico. This is a big task for Barcelona in this El Clásico but this contains risk for them too. Playing attacking against Real Madrid with many good attacking and speedy players, is very risky.
Xavi may be thinking about the best strategy to get the best results in the match later. But catching up with Madrid's points difference will be very difficult for Barcelona if you look at Madrid's remaining matches this season.
Even if Barcelona manages to win and get 3 additional points in the next match, I also doubt they can catch up with the points difference with Madrid. Even though there is still a chance, it will be quite difficult to achieve unless Madrid is really unlucky and has to perform badly in the next few matches.