Barca, having already won the first leg 5-0 at the Nou Camp, found themselves 2-0 down after five minutes in Seville on Wednesday and ended up losing 3-1 at the Benito Villamarin.
"The defeat against Betis will help us to grow," he said.
"In two weeks we have to play against Arsenal and that won't be easy.
"Losing can be good for you. When you lose in the Champions League, you realise what it takes just to be there - the defeat will be good for us."
Barca lead the league by four points at the halfway stage from fierce rivals Real Madrid, but Guardiola says that advantage means nothing at this stage.
"Leagues are never won midway through January or February," he said.
"There is a long, long way to go and it is very difficult to keep winning - our defeat (against Betis) shows that."