The speaker faces a sea of wonder too big to pull out and examine from the shore. The only way to know it is to go in, so they dive and explore. What they bring back to the surface is "breathtaking," yet the speaker feels it still falls short of the whole. A handful of treasures can't hold the sea.
That feeling pushes the speaker to dive a second time, and this time they don't come back up. The single word "Stayed," set alone on its own line, lands like a deep breath held and then released. The pause makes the decision feel quiet but final.
The mood is awestruck and a little hungry. There's no fear in the plunge, only curiosity and surrender. The sea can be read literally, but the poem seems to suggest something larger, such as an endless subject, a passion, or an experience that can't be summed up from the outside. Some things, the speaker implies, you have to live inside rather than carry away.