The main themes of the poems of wordsworth are nature,human mind's power,childhood,joyfulness,mystery,beauty of music etc.The themes were from humble and rustic life. He chose rustic language for his poetry.. According to Wordsworth, the language of prose and that of poetry are closely related with each other in their nature, function (utility) and appeal (application). 
Wordsworth deals with the question of where the meaning in our lives come from. He believed that it came from the relation with nature. it can be seen in many of his poems. He used to claim himself as the worshipper of nature.
The idea is a philosophy of peace, tranquility of mind,service to humanity etc..