This quote means that if you want to be a good writer, you need to write about things that you truly love. Do not just write for the sake of writing; find what you are passionate about and write about it. It is important to find joy in the process of writing, because that is what will motivate you to keep going. Love what you are writing about, and have a sense of purpose. You should have something to look forward to in the morning when you begin writing, and finding something you love to write about can help you be motivated each day.