Someone is renovating, and the speaker is watching the bricklayers tear up and rebuild a space. Instead of complaining about the chaos, the speaker treats it like a drink. The opening line, "drinking in," works two ways: taking in the sight with the eyes, and literally sipping. The disorder becomes something to savor.
The last lines turn this into a toast. "To it, to them" seems to honor both the mess and the workers who made it, and the "glass of alteration" suggests that change itself is what's being raised and swallowed. The broken, scattered lines on the page echo the disorder they describe.
The mood is playful and quietly celebratory. There's an acceptance here, even pleasure, in things being unsettled. The speaker seems to find the in-between stage, before anything is finished, worth appreciating on its own terms.