This imprisonment revealed in two ways the stuff of which William Penn was made. First severity was tried, and one day his servant brought him the report that the bishop was determined he should recant or die in prison. He only smiled and said, "They are mistaken in me; I value not their threats. I will weary out their malice. Neither great nor good things were ever attained without loss and hardship." Then they sent Stillingfleet, the future bishop, to try his powers of persuasion, but they, too, utterly failed. "Tell my father, who I know will ask thee, that my prison shall be my grave before I will budge a jot, for I owe my conscience to no mortal man." Such spirit, combined with the ability his books were revealing, revived the admiral's pride in his son. The court, too, began to take interest in him, and shortly after Stillingfleet's visit he was released, having been in the Tower more than eight months.
He at once resumed his preaching, and having been partially reconciled to his father, was employed by him to attend to his Irish estates. On his return home, his father received him fully into his favour, to the great delight of his mother's heart.
But soon trouble again overtook him, though only again to place him on a pedestal where his virtues and power would be more manifest, and where his voice would reach a larger audience. Going to the meeting-house in Gracechurch Street, London, he found it closed and guarded by soldiers. However the Friends held their service in the street, and for this W. Penn and W. Meade were indicted under the Conventicle Act. Hepworth Dixon regards this as "perhaps the most important trial that ever took place in England," and speaks of Penn as the great vindicator of the old charters and of trial by jury. He met the browbeating of the city magistrates with spirit and dignity, and encouraged the jury to do the right manfully. After twice returning an evasive verdict, and being locked up for forty-eight hours, the jury finally acquitted the prisoners. The court was greatly annoyed, and vindictively fined the jury for contempt. They refused to pay the fine and were sent to prison. Penn encouraged them to test the legality of this imprisonment, and the highest legal authority in the land decided against it and released the gallant jury.[9] A full account of the whole proceedings was published, and helped materially to encourage resistance to illegal interference with liberty.