Sobran comes from the verb sobrar, meaning "to be left over" or "to be in excess". It's a uniquely poetic word to find in a love song, offering a much deeper compliment than a simple adjective.
In the line "para describirte las palabras sobran", the singer expresses that to describe his love, words are simply not enough; they are superfluous. It's a powerful way to say that her amazing qualities transcend anything that can be captured in language, making it a truly beautiful and sophisticated expression to learn.
This song is a massive, heartfelt declaration of love. The title itself, "La Mejor De Todas," tells you everything you need to know: it means "The Best of All." The singer spends the entire song listing the reasons why his partner is absolutely perfect for him. He sees her as a literal gift from above, singing, "eres el regalo que bajó del cielo" [you are the gift that came down from heaven]. He's so completely in love that he even says, "hasta tus defectos me han enamorado" [even your flaws have made me fall in love].
He describes her as the main character in his life—"La protagonista de mi nueva historia" [The protagonist of my new story]—and the source of all his happiness. When they're together, time just melts away. He feels she has everything he could ever want, and he elevates her beyond a simple crush, calling her "alguien más que el amor de mi vida" [someone more than the love of my life]. It's a sweet, totally devoted song about finding someone you believe is truly incomparable.