This poem is an allegorical romance illustrating a moral and spritual journey through various trials and tribulations before ultimately attaining righteousness and glory. Each character represents some sort of abstract idea. For example, the fairy queen, Gloriana, is meant to represent Queen Elizabeth while the Red Cross Knight represents a truly good and Christian man. Lady Una represents truth and knowledge. Her parents (humanity) are held captive by the dragon (evil). So...what Spenser is saying is that humanity is held captive by evil and only truth and goodness will result in their freedom.