Of course even though it's a pre-season game this result is a warning to Madrid. Last season they also beat Madrid in the second match. This means that Barcelona is no longer like the beginning of last season. Xavi has indeed changed Barca for the better. They were able to prove last season ended in second position. In addition, this season's transfer market is used by Xavi to make Barca even more powerful. I think tomorrow they are candidates for the La Liga title.
Actually the threat will always be there, even though Barcelona struggled like last season. The key is they don't let their guard down and take lightly the opponents they will face, whatever club it is. The difference now is that the pressure will be even greater on Real Madrid. But if you look at the project for the long term, Real Madrid has an advantage over its rival, Barcelona. This match they also gave a little glimpse of what their line-up would look like next season.