Wordsworth was a foreward thinking, already noting the "revolution" that was happening as industrialization swept through England. In the late 1700s, the mechanization of many production systems and the new possibilities for trade helped to explode industry. People flocked to the cities for jobs in factories, knowing that they could make more money and better provide for their families than if they remained in the country. Rural and agricultural communities were changed forever by this emigration, as were family dynamics. Businesses and individuals were working longer and harder, and moving a much faster pace than was typical in pastoral England.
Wordsworth firmly believed that humanity was giving up its soul - and individuality - to the pursuit of money. "We have given our hearts away, a sordid boon!" The hearts became a part of the machinery of industry. When he says "we are out of tune", he is making a firm criticism of society's behavior. This is followed up by making what would have been at the time a controversial statement - that he would rather be a pagan (than a Christian) because, at least then, he would have harmony with nature and, thus, with himself.
Wordsworth helps to usher in the Romantic era of literature with this poem, when many more authors will extol the virtues of respecting and "being at one" with nature.