Generally rain symbolises emotions, release of feelings.
If the rain is gentle it is usually a relaxing experience and suggests a release from ideas and intellect. If it is a downpour and storm, it is feelings which may drench us, as in sadness or grief about a friend passing. If the land is inundated, then our common sense is lost to sight in the emotions released, and danger may threaten.
But rain may also show a return of feelings after a long spell of dry intellectualism or drought of feelings.
Some dreams show a massive downpour and feel that they have to wade through a flood, making it difficult to move; also it can be dangerous because visibility is poor. This suggests either emotions or natural events make it difficult for you get around as usual. A heavy falll of rain can also can be a start of very big changes in ones life and feelings.
If the rain is entering ones house it can signify worries about ones living conditions and comfort.
Rain can be a cleansing experience when it clears the ground and plant grow because they are watered. So it then represent a cleansing of worries or thoughts and emotions.
If a flood washes your house away or other things it may be that it is about a way of life, an attitude that has been destroyed or radically changed.
Idioms: Come rain or shine; it never rains but it pours; saving for a rainy day.