The speaker sounds oddly content. He calls himself a happy man, and the evidence he gives is simple: he plays in the garden until night falls. There's no grand event, just an ordinary pleasure enjoyed fully.
Yet the poem is edged with unease. The opening lines say the Lord is "as strange as the devil," which puts God and the devil on nearly the same footing, both puzzling and beyond understanding. The speaker doesn't try to solve that mystery. He simply sets himself beside it ("and me") and declares his happiness anyway.
The last two lines carry the surprise: every minute he expects to die. That could sound grim, but the poem treats it calmly. Awareness of death seems to sharpen his enjoyment rather than spoil it. The title fits this idea of living in the moment, since each minute might be the last. The mood is quiet, playful and a little eerie, with joy and mortality sitting side by side.