Thither, as Parker said, he "came to build up piety and morality; to pull down only what cumbered the ground." His main purpose to the last was to teach "the naturalness of religion," "the adequacy of man for his functions" without priestly aid, and, most important of all, that superiority of the real Deity to the pictures drawn in the orthodox creeds, which Parker called "the infinite perfection of God." He was singularly successful in awakening the spirit of religion in men who were living without it, but the plainness with which he stated his faith, in sermons which had a large circulation, called out many attacks. Prayers were publicly offered up in Boston, asking that the Lord would "put a hook in this man's jaws, so that he may not be able to preach, or else remove him out of the way and let his influence die with him." No controversy hindered his labouring systematically for the moral improvement of his hearers, who sometimes amounted to three thousand. His sermons are full of definite appeals for self-control and self-culture; and his personal interest in every individual who could be helped was so active that he soon had seven thousand names on his pastoral visiting list. Appeals for advice came from strangers at a distance, and were never neglected. Not one of the great national sins, however popular, escaped his severe rebuke; and he became prominent as early as 1845 among the preachers against slavery. He was active in many ways as an abolitionist, but was not a disunionist. He seldom quitted his pulpit without speaking for the slave; and every phase of the anti-slavery movement is illustrated in his published works. Pro-slavery politicians were as bitter as orthodox clergymen against him; and he describes himself as "continually fired upon for many years from the barroom and pulpit." His resistance to the Fugitive Slave Law caused him to be arrested and prosecuted, in company with Wendell Phillips, by the officials of the national Government.