The pen is a symbol of the speaker’s creative power. It is the manner in which he can express all of his ideas and intelligence and share them with the world so that he may remain even after his death.
The “night’s starr’d face” is a symbol for the unknown, but also possibility. The “symbols of a high romance” are cloudy and exist in shadows because he cannot know for sure what their true meaning is by just looking, but at the same time they do exist as a possibility for his life and he has a “chance” to try to decipher them and find his “high romance” in his life, given he has enough time.
The “shore of the wide world” is another symbol for possibility in the speaker’s life. He has the opportunity to fully dive in, live and explore, but standing on the shore is daunting with so much possibility because of the fear that he may not have enough time to accomplish all that he wants and is offered in the world with the short span of time that his life offers.
The reader can argue that the speaker is Keats himself, but more likely it is an unknown narrator/poet reflecting Keats’ fears, as well as those of the poet in general, whose main goals are to find inspiration through love, and write his legacy down so that he does not die before he feels that all of his creative power and intellect is used and he has written everything that exists in his brain.
At the heart of the poem is man reflecting on death, life, and time. At one point of another most human beings think about their impending death, even if that death is still far in the future. The speaker has a lot he wants to accomplish with all that the world can offer to him and his mind, and he fears he will not have enough time to achieve everything he desires.
Repetition is used to emphasize the speakers thoughts, and fears. We know that he is turning thoughts over in his mind and he is telling us, in a sort of list form, what it is that leads him to reflect on time and death: When I have fears, When I behold, when I feel, Before my pen, Before high-piled books, of unreflecting love, of the wide world. Those are some examples of the repetition Keats employs, once again emphasizing his continual thoughts that spark his fears, as well as making the urgency of time in the things he needs to accomplish “before” that time is taken from him.