At twenty-three, the speaker feels that Time has stolen his youth almost before he’s had a chance to use it. The days rush by, yet he hasn’t produced the poetry or shown the maturity he expected of himself. He suspects his outward appearance makes him seem more advanced than he really is inside, where he feels unready and lagging behind those who bloom earlier.
Then the tone shifts. He accepts that whatever his pace—fast or slow—it all moves toward a destiny set by Heaven. The poem ends with a quiet hope: if he remains faithful, all his efforts and delays are equal in the eyes of his “great Taskmaster,” God. The mood moves from anxious self-doubt to a calm, trusting surrender.