Loe builds the poem on one image: time as a vandal that slips into the heart the way a grain of sand slips into a clam. Like the clam, we can't get rid of the intruder, so we respond to it. The poem suggests that our long annoyance with time's passing is what produces invention, the "pearl" we make in answer to it. Human effort, in this view, is a way of stretching ourselves outward, shaping space around the self because we can't stop time.
The speaker's feeling is a mix of resentment and hope. Time is called a vandal and an irritant, yet the poem treats it as the source of something valuable. In the last lines, the future arrives like a wave breaking out of the "shell of now," and the speaker imagines reaching its shore. If that happened, they would be a "joyful jeweler," someone who turns pain into beauty. The mood is reflective and quietly optimistic, with a thoughtful, slightly wistful edge.