Franklin believed in God and in the social usefulness of religion, but he did not subscribe to any particular sectarian doctrine. This led him to help raise money to build a new hall in Philadelphia that was, as he put it, "expressly for the use of any preacher of any religious persuasion who might desire to say something." He added, "Even if the Mufti of Constantinople were to send a missionary to preach Mohammedanism to us, he would find a pulpit at his service."
He also wrote parodies that poked fun at Puritan intolerance. In one of them, called "A Witch Trial at Mount Holly," a couple of accused witches were subjected to two tests: weighed on a scale against the Bible, and tossed in the river with hands and feet bound to see if they floated. They agreed to submit--on the condition that two of the accusers take the same test. With colorful details of all the pomp, Franklin described the process. The accused and accusers all succeed in outweighing the Bible. But both of the accused and one of the accusers fail to sink in the river, thus indicating that they are witches. The more intelligent spectators conclude that most people naturally float. The others are not so sure and resolve to wait until summer when the experiment could be tried with the subjects unclothed.
Franklin's freethinking unnerved his family. When his parents wrote of their concern over his "erroneous opinions," Franklin replied with a letter that spelled out a religious philosophy based on tolerance that would last his life. It would be vain for any person to insist that "all the doctrines he holds are true and all he rejects are false." The same could be said of the opinions of different religions. He had little use for the doctrinal distinctions his mother worried about. "I think vital religion has always suffered when orthodoxy is more regarded than virtue. And the Scripture assures me that at the last day we shall not be examined by what we thought, but what we did ... that we did good to our fellow creatures…"
By the end of his life, he had contributed to the building funds of each and every sect in Philadelphia, including £5 for the Congregation Mikveh Israel for its new synagogue in April 1788. During the July 4 celebrations that year, he was too sick to leave his bed, but the parade marched under his window. For the first time, as per arrangements that Franklin had overseen, "the clergy of different Christian denominations, with the rabbi of the Jews, walked arm in arm."
And when he was carried to his grave two years later, his casket was accompanied by all the clergymen of the city, every one of them, of every faith.”
--Walter Isaacson, Citizen Ben’s 7 Great Virtues (Time Magazine, July 7, 2003)