The match is being staged in Jeddah, Saudi Arabia, on Wednesday night.
Valverde said on Tuesday: "The trophies I have won with Athletic are the ones that mean the most in my life. No doubt about that," Valverde said before Wednesday night's match.
"With regard to the Supercopa, it's true that, as it's a smaller competition, it doesn't have the pedigree of the Copa del Rey or LaLiga.
"Before, it was played over one game, then two, now there are also four teams, but it has always meant a lot to us when we've won it.
"We have won it twice in recent year and the one I was involved in was our first trophy in many years. Trophies make clubs bigger, that's what all the other teams here think. We have to do everything we can to win it.
"We're excited about the Supercopa. We've been looking forward to it for a long time. Our intention is to make the most of our chances and try to win it."
He continued: "It's a tough match against a huge opponent. Barça were cruising and hard to reach in the first part of the season. They haven't gotten such great results in the last month and a half, but they look good and play with a lot tempo.
"We're not the favourites, but we have to go for it, we've come all this way and we're going to give it everything we've got.
"We're feeling good. We try to approach matches in such a way that we can be competitive in all of them. We have the belief to think we can beat anyone, but the humility to know we have to be solid and at our best to make that happen.
"We're not going to fool ourselves. Every time you overcome a difficult test, you gain confidence in what you do. Everything we've achieved this year has reinforced our belief in what we're doing."
The gaffer is expecting a great atmosphere at the stadium, saying: "We haven't seen too much so far, but we know there will be a lot of people.
"I played my last match with Barça here and there was a great atmosphere. I hope the fans enjoy themselves and that we can put on a good show for them."