Very huge blow for Barcelona because dropping points mean that Real Madrid will remain at the top of the table and whenever Real Madrid is topping the league table in the early stage of the season, it's always hard for them to give it up accept when the league has gone far. Barcelona has problem in their defense that is why they conceded goals in all the three games they have played so far. Rayo Vallecano were also determined in this game which is why they could equalize and almost won Barcelona but the match ended 1:1. The season is still new anyways, within mid season we will see how the league table will look like, if Barcelona or Real Madrid will be at the top.
Anything can still happen in the future, the situation can change throughout the season. It is indeed very disappointing to see Barcelona fail to secure full points today, and it has been proven that their defense is quite weak. Hansi Flick must find a solution to this problem, although overall, Barcelona still looks quite solid.
Rayo Vallecano managed to utilize their home match very well, they were quite disciplined in defense, so Barcelona didn't have many chances for threatening opportunities. On the other hand, I don't think this draw will necessarily make Real Madrid comfortable at the top of the standings, as there are still many matches ahead.