The sonnet begins with both apostrophe and personification, as the speaker directly addresses time itself. By using the word "devouring," the speaker invites readers to see time as an all-consuming, destructive force that ravages everything in its path.
To further demonstrate time's might, the speaker goes on to say, "blunt thou the lion's paws." Lions are very powerful and strong animals, and the fact that time is capable of dulling their sharp claws implies that even the fiercest, most fearsome creatures on earth are no match for time, which gradually weakens everything in its path. In other words, age inevitably brings on decay, as everything that was once glorious and strong eventually loses its edge.
This, it seems, is simply the way the world works—an idea the speaker highlights by personifying the earth, saying, "And make the earth devour her own sweet brood." This phrase repeats the word "devour," emphasizing the idea that time lays waste to everything and that experiencing this kind of ruin is simply part of being alive.
The metaphorical idea of time forcing the earth to eat "her own sweet brood" also implies that the earth itself is bound to time in unavoidable ways—that life on earth is defined by the passage of time.
These opening lines also establish the poem's use of iambic pentameter, a meter in which lines contain five iambs (metrical feet consisting of an unstressed syllable followed by a stressed syllable: da-DUM). However, the first two lines contain two metrical substitutions:
Devou- | ring Time, || blunt thou | the li- | on's paws,
And make | the earth | devour | her own | sweet brood
For the most part, there is a strong iambic rhythm in these lines, as phrases like "And make the earth devour" feature the da-DUM da-DUM da-DUM thump created by a string of iambs. And yet, these lines also include two spondees, which are metrical feet consisting of two stressed syllables. For instance, the words "blunt thou" in the first line create a spondee, as do the words "sweet brood" in the second line.
This subtly disrupts the iambic rhythm, but it doesn't totally upend the overall feel of the poem. Instead, these spondees indicate that the poem won't perfectly follow its own meter, effectively leading to a slightly off-kilter feel that perhaps reflects the speaker's discomfort with the fact that time lays waste to all.