This quote from Seneca is a metaphorical way of expressing the importance of having clear goals and direction in life. In the metaphor, the “port” represents the goal or destination, while the “wind” represents the opportunities, circumstances, or resources that can help one reach their goal. Seneca is saying that if a person doesn’t know where they’re going—if they don’t have a clear goal or purpose—then no opportunity or circumstance will seem beneficial or favorable, because they won’t know how to use it to their advantage. They’ll be adrift, like a ship without a destination, at the mercy of the wind and waves.
Conversely, if a person has a clear goal or purpose, they can take advantage of opportunities and circumstances (the favorable wind) to help them reach their goal (the port). They can chart a course and adjust their sails to make the best use of the wind, no matter which direction it’s coming from. So, in essence, this quote is a call to reflection and self-awareness. It encourages us to clearly define our goals and aspirations, because only then can we recognize and utilize the opportunities that will help us reach them.