I'm choosing to write about the poem, "Mezzo Cammin" because so far it is my favorite poem in the poetry packet. The speaker is a man at the middle of his life, reflecting upon his youth and all of the things he has yet to achieve. He sees what he has not done as missed opportunities and reflects that he still wants to do all of the things he once set out to do.
The occasion of this particular poem is obvious, with the man's (or possibly Longfellow himself) life reaching its midway point, he cannot help but to ruminate about his life's successes and failures. The man sees that he has not lived his life to its fullest, but also that he has the opportunity to change. In that way, the audience isn't limited to middle-aged people, but is universal in telling all people that they should continue to strive toward their goals, and should neither see themselves as too old to do good or young enough to have time to put off their dreams.
The full meaning of the poem then, I think, is that however old we are and whatever our dreams may be, we should always strive to live life to the fullest. Longfellow achieves this meaning by using the extended metaphor of comparing life to climbing up a hill. He refers to his past as something that happened at the bottom of the mountain and anticipates "the cataract of Death far thundering from the heights" in his future. This way of seeing life as fleeting and death as impending is both discomforting and motivating, but Longfellow ultimately achieves his goal of simply showing that life is ephemeral.