The original building was of but one story, with gable ends. When alterations were made in 1837 the top of the church was raised bodily, while a larger roof was built over the old roof. The visitor who climbs to the loft is able to see the old walls and windows. The floor was raised one step above the street level, and was paved with brick. Rev. George Duffield, D.D., who was pastor from 1772 to 1790, was a prominent figure during the Revolution. He was chaplain of the Continental Congress and of the Pennsylvania militia during the period of the war, and he delivered fiery messages that stirred patriots to action. John Adams, who was a member of the church, called him a man of genius and eloquence. On May 17, 1776, after listening to a sermon in which Dr. Duffield likened the conduct of George III to the Americans to that of Pharaoh to the Israelites, and concluded that God intended the liberation of the Americans, as He had intended that of the Israelites, he wrote to his wife: "Is it not a saying of Moses, Who am I that I should go in and out before this great people? When I consider the great events which are passed, and those greater which are rapidly advancing, and that I may have been instrumental in touching some springs, and turning some small wheels, which have had and will have such effects, I feel an awe upon my mind, which is not easily described. Great Britain has at last driven America to the last step, complete separation from her; a total, absolute independence...." Headley, in "Chaplains and Clergy of the Revolution," says: "The patriots of the first Congress flocked to his church, and John Adams and his compeers were often his hearers.... In a discourse delivered before several companies of the Pennsylvania militia and members of Congress, four months before the Declaration of Independence, he took bold and decided ground in favor of that step, and pleaded his cause with sublime eloquence, which afterwards made him so obnoxious to the British that they placed a reward of fifty pounds for his capture." Later on in the same sermon he prophesied: "Whilst sun and moon endure, America shall remain a city of refuge for the whole earth, until she herself shall play the tyrant, forget her destiny, disgrace her freedom, and provoke her God." As chaplain of the Pennsylvania militia, Dr. Duffield was frequently in camp, where "his visits were always welcome, for the soldiers loved the eloquent, earnest, fearless patriot." Headley gives this incident of the courageous chaplain's work: