Three short lines set a quiet scene: a May morning, a high tide, and one person watching the sea by himself. The speaker doesn't describe the water or the beach in detail. Instead, the poem turns on its last phrase, "my bachelor eye," which shifts attention from the view to the one doing the looking.
"Bachelor" is an unusual word to attach to an eye. It suggests an unmarried, unattached way of seeing, one that takes things in without anyone else beside it to share or interrupt. The speaker seems to be alone, and the poem leaves open whether that feels peaceful or a little wistful. Probably it's both. The high tide, full and brimming, makes a contrast with a single person standing apart from it.
The mood is calm, spare, and slightly wry. There's pleasure in the spring morning and the open sea, along with a gentle awareness of solitude. Because the poem says so little, the feeling comes through in the quiet and the odd, memorable phrase at the end.