A person sits alone on a quiet afternoon, and the poem treats the afternoon almost like a companion. "Alone together" is a small paradox: the speaker isn't lonely, just content to share the hours with time itself. The mood is relaxed, a little dreamy, and gently funny.
The humor arrives in the second stanza. The speaker's calm, their "Zen," comes with wine, which is a playful admission that this peacefulness isn't strict spiritual discipline. It's more of a pleasant, indulgent mellowness. Then the Zen is "sent home on foot," as if it were a guest who has had a bit too much and must walk back unaided. The image suggests that the clarity wine brings is temporary and a little unsteady, and that the speaker knows it.
The title, "Zennish," fits this tone: not truly Zen, just Zen-ish. The speaker seems to feel contentment mixed with wry self-awareness, taking pleasure in the moment without pretending it is more profound than it is.