I have two simple questions:
In the sentence:
"There is no greater thing to do than follow your passions in a way that serves the world and you."
Why should we say "follow" and not "following"? As it says "passions" why does "serve" have an "s"?
Why should we say "follow" and not "following"?
Because "continuous" verbs are effectively adjectives, and a verb is needed in that position. It's an imperative phrase there, "follow your passions"
As it says "passions" why does "serve" have an "s"?
Because the "way" (the method or manner in which you go about your passions) is a singular, and that's what's doing the serving.