Chinese idioms have deep meanings and they often use a figure of speech to express a point. The Chinese calligraphy painting of generosity is one very good example. The idiom means oceans are big and can accept many streams. It encourages people to be generous and try to accept people who they don't like.
Chinese calligraphy painting of an idiom of generosity, using vast oceans as a figure of speech about open minded people. , An Ocean Accepts 100 Streams Chinese Calligraphy Scroll by Other Artists.