I think that Max wants Liesel to know that her words are powerful. The tree in the story represents Liesel and her words, thoughts, and ideas. And that’s why it is constantly growing more and more. Words have more power than we think, and when we use them right they can change the mindset of tons of people. Like Hitler was voted into his position just by using the right words that the Germans want to hear. The story said that he didn’t even have to weapons, he just had to use his words, he just had to make people believe that his words were the right ones. And then you have Liesel who sees right through him.