Bartra has stepped into first-team action this season following injuries to Carles Puyol, Javier Mascherano and Gerard Pique, making nine appearances in all competitions.
And after another of his Barca team-mates, Cesc Fabregas, withdrew from Vicente del Bosque's squad for the friendlies against Equatorial Guinea and South Africa, Bartra was drafted in for the first time.
"It was a very nice surprise to be in my first call with the seniors," he said. "It's a dream for me.
"It is important to feel at home here, not only with the Barcelona players, but with league rivals.
"The most important thing is to serve the team and add to that we remain the best team in the world."
Fernando Llorente became one of five strikers in the squad when he was named as Diego Costa's replacement for the friendly matches, and the Juventus striker is ready to perform.
"There are very big name forwards who can be here," he said. "We will all give the best we have.
"In every game you play in the national team you have to make the most of it."
Spain face the central African nation on Saturday before travelling to South Africa on Tuesday.
