Messi has just returned from an extended holiday after the World Cup, in which his Argentina side crashed out in the quarter-finals following a disappointing 4-0 defeat at the hands of Germany.
"The World Cup affected me a lot because I hoped for more," he told reporters in South Korea, where Barca are currently on a pre-season tour.
Nevertheless, the 23-year-old says he has recovered from that disappointment and believes Barca will be a force again next season.
"I have recovered and I am only thinking about Barcelona now," he said.
"The aims are always the same. This year we will be going for all the titles. We know it's difficult but we have a great squad.
"The group is keen to get going again and we are in good shape to get started."