Barca failed in their bid to retain the Liga title - a final-day 1-1 draw with Atletico Madrid handing the title to Diego Simeone's men.
The Supercopa de Espana represented Barca's only silverware in a frustrating season under Gerardo Martino, with the coach departing Camp Nou upon the campaign's conclusion.
Messi himself also endured a tough season, spending time on the sidelines due to recurring hamstring injuries.
Despite that, the star attacker struck 41 times in 46 appearances.
And he hopes that a switch in focus will not be hard to come by as Argentina seek a first world crown since 1986.
"I know that now I'm here with the national team I'll change my frame of mind," Messi told reporters after touching down in Buenos Aries on his way to meeting up with the squad.
"As often happened the other way round, when things didn't go so well with the national team and then I went back to Barcelona and played well.
"Let's hope it's the other way around this time.
"When I get together in preparation with my team-mates, with my friends, then it'll change my headspace and things will change.
"We have a great group. We're all coming into it on good form and hopefully we can achieve our objective. The national side is very strong."
