Almost every line here sets two things against each other: a single drop and a whole sea, tears and happiness, a tiny match and burning countries. The poem works like a list of contradictions, and the short, clipped lines make each pairing land quickly, like a series of small shocks.
The speaker seems tired of surfaces. Some pairs show how small things can grow huge, while others show emptiness hiding inside something that looks full, like a flower held in the hand that is somehow lifeless, or a plate of food next to an empty stomach. The lines about "sweet life" being dead and a remembering heart that will forget suggest that even our deepest feelings can turn on us.
The closing couplet states the point plainly: nothing in the world is quite what it seems. The mood is quietly disillusioned, a little bleak, but also watchful, as if the speaker is urging us to look beneath appearances, even behind our dreams.