This is only the first stanza of a much longer poem by Henry Wadsworth Longfellow. The title of the poem is "A Psalm of Life." Despite the title, we would not call this poem "a psalm," but rather simply "a poem." The full text is at: https://www.poetryfoundation.org/poems/44644/a-psalm-of-life In this first stanza, the poet seems to be arguing with an imaginary person. This person has apparently said something like "Life is meaningless. It's an empty dream. In the end we all die, so what does any of it matter?" The poet retorts "Don't tell me that life is but an empty dream." The message of the rest of the poem says that even though we die, our life has meaning. The next line says "the soul is dead that slumbers." In ordinary word order it would be "the soul that slumbers is dead." This refers back to "empty dreams." I think the idea is that the soul that slumbers might as well be dead already. (A modern, colloquial expression with a similar meaning is "If you snooze, you lose.") "Things are not what they seem" means what it says. Yes, life may seem meaningless at time, but it is not. The next stanza is: Life is real! Life is earnest! And the grave is not its goal; Dust thou art, to dust returnest, Was not spoken of the soul. The first two lines are often quoted. He says you are in the world to do more than just daydream and die. The second two lines refer to a famous verse from the Bible says "for dust thou art, and unto dust shalt thou return." The poet notes that this verse refers to the body, not to the soul. A later pair of lines encourages us to "leave behind us," when we die, "footprints on the sands of time." At the end he encourages us to be "up and doing," and to be busy achieving, trying to leave our mark on the world. In short, it is a motivational, inspirational, positive-thinking poem.