The central idea of Wordsworth's 'The Rainbow' is that the sort of person we are when we are young determines the sort of person we grow up to be. The idea is contained in the poem in the line: "The child is father of the man." Wordsworth believed that being good made you a better person, while being evil made you a worse one. If he had lived a century later people might have called him an existentialist.

'The Rainbow' symbolizes the life sustaining and life nourishing goodness of Nature. The sight of the beautiful rainbow which Wordsworth saw when he was only a child is deeply etched in his memory and the same joy that he experienced when he saw it as a child, contiunes to remain with him through his adulthood. He desires that this same childhoood joy should continue to sustain him even in his old age. Wordsworth says that he would rather die than not being able to experience the same joy that he experienced when he saw the rainbow when he was a small boy after he becomes an old man. The memory of the beautiful rainbow and its pleasant associations form the link between his childhood, adulthood and his old age:past, present and future. Wordsworth concludes the poem by expressing the desire that each day of his existence be linked with the next by beautiful and simple natural sights like the rainbow. The theme is that childhood experiences become the foundation for all adult experiences.