Fire is usually something we fear, but this short poem asks us to look at it as something beautiful. The speaker invites the reader to "gaze" at flames, and the command feels almost gentle, like pointing out something wonderful in the sky. The flames "seem to blossom in the air," so fire becomes a flower opening up and spreading its petals.
Then the last line changes the picture. The fires "burn gardens," which means the thing being compared to a flower is destroying actual flowers. The blossoms in the air exist because blossoms on the ground are disappearing.
The speaker never says outright how they feel, and that is what makes the poem unsettling. The tone is calm, even admiring, yet the ending carries a quiet sense of loss. The mood sits somewhere between wonder and unease. We are drawn to look at the fire, and we feel a little guilty for finding it lovely.