Penitencia translates to "penance" or "atonement." It's a word with strong religious connotations, referring to an act performed to show sorrow for sin or wrongdoing.
In the song, the lyrics declare, "Y si quererte es pecado pues yo ya valí / Que venga la penitencia" (And if loving you is a sin, then I'm done for / Let the penance come). This dramatic use of the word elevates the forbidden love to a profound, almost spiritual, level, making it incredibly enticing and memorable.
"Beso Prohibido" is about a love that everyone around the couple insists is a mistake. The narrator admits he might look like the worst possible match for her, calling himself a "forbidden kiss" and a "bad deal," but he refuses to accept anyone else's verdict on their relationship.
Even though he and his partner are opposites - "you are water and I am fire" - he argues that's exactly what makes their bond work. No one else understands what it feels like to be caught up in this connection, and no one else could love her the way he does.
The chorus turns the criticism into a promise: he'll let people keep talking, and he'll silence their doubts simply by being happy with her. It's a song about choosing a love that isn't easy to explain to other people, and trusting it anyway.