Sagrado translates to "sacred" or "holy". It's a beautiful word that adds a deep, spiritual dimension to the song's promise of love.
Enrique Iglesias sings, "Como fuego sagrado, te guardaré" (Like a sacred fire, I will keep/protect you). By comparing his love to a sacred fire, he's promising that his feelings are pure, eternal, and will be protected at all costs, no matter how long he has to wait.
This song is a beautiful, dramatic promise to a lover who is leaving. Enrique Iglesias lays out a simple deal: if she swears she'll come back, he will wait for her, no matter what. He tells her, "Si juras regresar / Si prometes volver / Con los ojos cerrados / Te creeré" (If you swear to return / If you promise to come back / With my eyes closed / I will believe you). It's a song about total, almost blind, faith in someone.
He promises to protect their love like a "fuego sagrado" (sacred fire) and believes that "Nuestro amor nunca va a morir" (Our love will never die), even with the distance between them. He imagines her dancing just for him, a sweet image that shows how connected they are. The whole song is one big declaration of loyalty, promising over and over, "Pase lo que pase / Aquí estaré" (Whatever happens / I will be here).