Rendeu-se comes from the reflexive verb render-se, which means "to surrender" or "to give in". It’s a powerful, dramatic word that adds a touch of epic romance to the song.
In the lyrics, Matias Damásio sings, "O mundo rendeu-se ao nosso sorriso" (The world surrendered to our smile). He uses this verb to describe a love so powerful and joyous that it captivates and conquers everyone and everything around it, making it seem almost legendary.
This song is a huge celebration of a love so big it feels like the whole universe is cheering you on. Matias Damasio sings that even famous poets couldn't find the words for this feeling, because "Anjos aplaudem nosso amor" [Angels applaud our love] and "Até Deus sorriu pra nós" [Even God smiled at us]. It's about being so full of love that your heart feels like it will explode and your voice gets hoarse from shouting "te amo" [I love you].
The main idea, though, is that when you're this in love, other people might not get it. The chorus repeats, "Mas o mundo nos chama loucos" [But the world calls us crazy]. Why? Because they do things like talk to themselves on the street and count the stars in the sky. It's a song about being so happy and wrapped up in your own world with someone that you don't care if anyone else thinks you're a little bit mad. The final advice is simple: "Mas não liga não" [But don't pay it any mind].