This quote means that simply having ambition and talent alone isn’t enough to be successful. To really achieve success, one also needs to have a strong passion for and dedication to the activity or task that they are trying to accomplish. A “vocation” is a strong feeling of being called to do something, and having a sense of purpose. So in order to have true success in whatever endeavor you choose to pursue, it is important to both love and believe in what you are doing.