Dave Bonta's "Tectonic" is a tiny poem that treats love like a force of nature. The speaker addresses a "you" and says that this person was the "first sea" making sand, the slow grinding of water against rock that turns mountains into beaches. The image suggests something enormous and patient, working over time rather than all at once.
The line "heart / hardly seen" can be read a couple of ways. Perhaps the beloved's feelings were hidden, or perhaps the speaker's own heart went unnoticed while it did its work. The poem leaves that open. What it does make clear is the result: this force was "carving a body into / the exact world," as if the beloved shaped the speaker, or shaped a person into someone fitted precisely to reality.
The mood is quiet, awed, and a little mysterious. There's gratitude here, but also a sense of scale, as though the speaker is looking back at how deeply one presence changed everything, even though it happened slowly and almost invisibly.