Arsenal's perfect start to the league campaign ended with a 3-1 loss to Liverpool at Anfield.
Unai Emery's men have kept one clean sheet in three Premier League games to start the season and David Luiz said defensive improvement was key.
"We have to [bring the number of goals down]. I think if you concede a lot of goals you cannot fight for the title so this is one main thing we have to think about and try to reduce and try to make the team stronger," he said. "It is not just about me, it is not just about the defenders, it is about the mentality of the team."
David Luiz gave away a penalty during the loss to Liverpool, while the former Chelsea defender was also beaten by Mohamed Salah for the third goal.
The 32 year-old believes it could have been a different game had Arsenal taken their chances to grab the lead against the European champion.
"I think the team already did great against Newcastle, did great against Burnley to understand the kind of game we were playing for," Luiz said. "We were clinical in Newcastle with one clear opportunity we scored and didn't concede.
"With Burnley, we were clinical to understand the game is always to play first ball, second ball, fighting. They tried to score with free-kicks and things like that and we did amazing and [against Liverpool] I think it could be a different game if we scored [first] but we did not and so this is about football.
"Football is like that. Every week is a new history and we have to try and learn and improve our game."