The 25-year-old Atletico Madrid forward says he owes his career to his adopted country, though admits switching allegiance from Brazil to La Roja was a difficult decision
Costa's international future had been at the centre of much speculation, with both Brazil and Spain stating their desire to select the 25-year-old, who has dual-nationality after residing in Spain for more than five years.
On Tuesday the Atletico Madrid striker declared his intention to play for the reigning world and European champions, provoking the ire of Brazil boss Luiz Felipe Scolari, and has now explained his reasoning, expressing his desire to repay the country he feels is responsible for his football career.
"I hope people understand and respect my decision because it has been very difficult," he told Atletico Madrid's official website.
"It was very difficult to choose between the country where you were born and the country that has given you everything.
"I looked at everything and saw that it was right and best to play for Spain because this is where I have done everything. All that I have in my life was given to me by this country.
"I have a special affection. Here I feel very appreciated for all that I do and I feel the love of the people.
"I hope people understand because it is not something against Brazil.
"I have family in Brazil and it is the country where I was born. I hope that God allows me to live there again in the future."
Spain boss Vicente del Bosque told AS Costa's decision was "good news" for la Roja, with the striker expected to be called up for the nation's friendlies with Russia and Gabon.