From the Super Mario Wiki
When Luigi sees Obi-Wan Cannoli, he tells Mario who he is, which causes Mario to recognize him as "the famous spirit who helps people who are about to get pounded" and to ask for his help. Obi mentions how he came on short notice and requests to be filled in on the details of the situation.
Mario explains that Tulio wishes to beat him up due to him asking Tulio's sister on a date and then asks what his first lesson is. Obi explains to Mario that "when you can pass through a wall, the path to enlightenment will be clear." Mario then rams into a brick wall, which instead of passing through, he sends several bricks flying from and knocks himself unconscious.
As Obi continues to lead Mario down the path of enlightenment, Mario is completely in the dark as to what he was supposed to be learning. After Mario starts arguing with Luigi for accidentally bumping him and ruining his "stork pose," Obi says that they're ruining his afternoon and that "those wishing to attain enlightenment should pipe down."
After Mario's attempt to ward off Tulio by pretending to be on crutches fails, Obi tells Tulio nobody is there, that he should forget about pulverizing Mario and that "you should be happier to be rid of your sister, she is a pain."
Sounding as if he was hypnotized, Tulio calls Mario his pal and leaves as Luigi looks on in shock.
As Mario thanks Obi, he asks him how he got rid of Tulio, and Obi explains that he "makes his voice echo and sound bossy." When Mario asks what he should have learned from this, Obi explains "Some people like Tulio grow strong and firm like a mighty oak. Some grow round and soft like a ripe tomato." When Mario asks what that means, Obi says Mario "makes a better tasting sauce than Tulio," and disappears.