but in the last several decades there has been a consensus forming on how to understand them. Freud had a few things right and a lot of things wrong. Jung was a little more profound but his concepts only fit a portion of dreams.
When you get into individual dreams and try to understand where the images and characters came from, they are very idiosyncratic and often come from very recent events. While they often turn out to have a clear meaning, it usually doesn't come about by applying an external theory.
They're making a lot of progress on the biological angle, but like any other complex, emotional process, dreams are not likely to be reduced to a biological phenomenon. They're probably closer to literature or art.