In Moana the plot is about a main character (Moana) who is returning the heart to Te Fiti to... well, prevent the world's end. Here's the order of events:
- Long before the story Maui steals the heart and loses it and it falls into ocean water.
- Then when Moana is a child the ocean pushes the heart to the island shore right into Moana's hands.
- Moana is immediately distracted, so her grandmother takes and stores the heart.
- Moana gets older, the island is in danger, Moana takes the heart, goes to find Maui, they together return the heart and the ocean is assisting Moana all the time.
So basically the ocean first delivers the heart to Moana, then accompanies her all the way to Te Fiti and keeps assisting her all the way.
Why coudn't the ocean just deliver the heart to Te Fiti instead?