PLEASE HELP ME understand this POEM!?

This poem, "The Chimney Sweep", by William Blake is about Blake's distain for the Church and culturally religious or subjective thinking. He once wrote in praise of lucid, objective thinking, "If the doors of perception were cleansed, every thing would appear to man as it is, infinite." Edwin Powell Hubble wrote, "Equipped with his five senses, man explores the Universe and calls the adventure Science". In the second stanza above, Blake mentions objective, healthy naturalness in the heath and the purity of winter's snows. He contrasts that lucidity with the blackness of the chimney-sweep, blackness that is the soot or foulness of man's subjective cultural deviancy from natural purity or truth. These were brave thoughts to utter in Blake's times.