Barca beat Bayern to the signature of the United States right-back, who joined from Ajax in a deal that could eventually cost the Catalan club €26million.
Dest signed a five-year contract with a €400m buyout clause, opting for Barca despite them being thumped 8-2 by Bayern in the Champions League quarter-finals last season.
"Bayern are a great club and there was interest from them, but I followed what my heart told me to and for that I signed for Barca. I think it was the right decision," Dest told a news conference.
"They are a club with so much history and I've always wanted to play here."
Dest is naturally relishing the prospect of playing alongside Messi, who opted to remain at the club for another season after a failed attempt to invoke a clause allowing him to leave for free.
"It's amazing to play with the best player in the world, Lionel Messi, I looked up to him," Dest added.
"I will run as much as I have to, I will run for everybody in the team. It will be so exciting to meet the best player in the world."
Dest is the first American to play for Barca. Born to a Dutch mother and a Surinamese-American father in Almere, he elected to represent United States over Netherlands.
But he still cited Koeman, who left his post as Netherlands boss to take over Barca following Quique Setien's exit, as a factor in his decision.
"Koeman of course was an influence, because he's Dutch and it will be easier to communicate with him," Dest said.
As for his inspiration, Dest is looking to emulate Dani Alves, who was the right-back for Barca in each of their treble-winning sides under Pep Guardiola and Luis Enrique.
Dest, who could make his debut against Sevilla on Sunday, explained: "If I can play this Sunday, it would be great, because I want to start as soon as possible.
"My role model was Dani Alves, a really good player at right-back, same position. Watching his clips on YouTube, I learned a lot from him and I can still learn a lot from him because his team-mates are over here like Lionel Messi and I can ask for advice. I want to be a player similar like him."