Each of the stanzas takes place during a different season. The poet can't seem to make up his mind what as to what season he'll end up dying in, so he hedges his bets and imagines all the possibilities. In the first stanza, he imagines dying during spring; the third is summer; and the fourth is winter. Strangely, winter isn't the bad guy here – in most poems about death, you'd expect winter, or at least autumn, to play a big role in setting the mood, but that's not necessarily the case here.