What is the main theme of fern hill?

Time in “Fern Hill” is so omnipresent that it’s often personified, acting as a playmate for the speaker of the poem. At first, time favors the speaker, allowing him to play freely and happily, but inevitably, time robs him of his childhood joy. Time is in control throughout the poem—though it “lets” the speaker play at ease, it is ultimately the authority that demands the loss of his innocence and exiles him from his Eden.