The boat is used here as a metaphor for teaching: a good teacher is like a boat, taking students from one side of the river to the other. In modern society where teaching is often just another profession, it is sometimes forgotten that teachers are pivotal to the development of contemporary and future societies.
Teachers - whether they work in a specific educational system or play a role as a mentor - can influence the thought and values of younger generations, and their teaching can change people's understanding and view of the world.