Sometimes sad people try to supress their problems and worries but Keats tells us to accept melancholy and pain. In the first line he instructs the reader not to go to Lethe to forget his sorrows so that the sorrows are kept, we should not escape pain. There are a lot of referrences to poison - but always in conjunction with negating words, as for example "neither twist Wolf's bane- (line 1-2). Eating poison might remind the reader of suicide very often commited by unhappy people, but the negating word forbids us to drown the sorrow that way. Again we are instructed to welcome melancholy.
Keats also determines the consequences of the escape from melancholy, "the wakeful anguish of the soul- (line 10) will be drowned. The drowned soul is a synonym for dulled consciousness which is negative.
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The second stanza tells us to enjoy beauty containing joy and pain.
The first four lines describe rain literally. Keats compares melancholy to rain creating both negative and positive images we associate with dolor. For example the "weeping cloud-, the rain which stands for sadness fosters the flowers. At the same time "to foster- and "flower- are words suggesting positive feelings. However the flower is "droop-headed-. In fact a flower is droop-headed when it did not get any water for a long time. In this case the rain nourishes it, droop-headed is not completely negative, the flowers are able to liven up. Melancholy falls from heaven and nourishes the flowers, it keeps the flowers alive. This means melancholy is essential and cannot be separated from joy!.
But these lines also evoke an image of mourning. Droop-headed also means to be sad. According to this fact the flowers are sad, the clouds are weeping, the hills are covered, the whole world is in mourning.
A similar image is given in line 14, "green- and "april- may mean spring and fertility, but the rain hides the "green hill- in a "shroud- which is a reference to death.
