Three short lines, and the whole poem is a gesture of humility. The title, "Strix," is the Latin word for owl (and the name of a genus of owls), so the "god" in the first line seems to be the owl itself, though the poem never says so outright. That is part of its charm: it lets the idea settle slowly.
The owl is called "odd as the world," which treats strangeness as something the bird shares with everything around us. It also "practices" a "great joy," a word that makes joy sound like a discipline, something done patiently and with skill, the way an owl hunts or waits in silence.
The last line turns to the speaker. "Give ground" can mean stepping back out of respect, or yielding territory. Either way, the speaker feels awe rather than ownership. The mood is quiet, reverent, and a little playful, as if the speaker is stepping aside at a meeting with something far older and wilder than he is.