"It would mean a lot for me to be a world champion," he said.
"It would be fantastic to win this trophy - and now there is a good chance, not just from a personal perspective but for Manchester United.
"We might only have one opportunity and we have to take it."
Ronaldo knows the bare minimum about Sunday's opponents, Ecuador's South American club champions LDU Quito.
They were not that impressive in beating Pachuca in Wednesday's semi-final, but Ronaldo knows any club capable of overcoming the might of Brazil and Argentina must be respected.
"We are expecting a difficult game," he said.
"The second match is always more difficult than the first, and we have to prepare well.
"Quito are a good team, with a lot of experience.
"We have a couple of days to study them and to see who the best players are, but the most important thing for us is to put the ball in the net."