This imprisonment, in the ordering of God's providence, brought to the right issue the great crisis of his life. In the same room with him in Edinbro' Castle was imprisoned Sir John Swintoune, who from a soldier and a Presbyterian had become a thorough Quaker. He was so zealous in propagating his opinions that the only way to silence him was to keep him in solitary confinement, which was at one time done for several weeks. No wonder, then, that he urged on David Barclay the full acceptance of the truth. On leaving the Castle, the colonel seems to have remained in Edinbro' even after he had sent his son, in company with a Quaker, David Falconer, to Ury. In Edinbro' he came out as an acknowledged Friend. He tells us what points satisfied his sober and careful judgment that the Quakers were right. He was struck with the correspondence between their peace principles and Isaiah's prophecy, that in Gospel times they would beat their swords into ploughshares, and their spears into pruning-hooks. Then again, they were all as brothers, loving and standing by each other, and had not Christ said, that his disciples should be known by their mutual love? The courageous soldier was in sympathy with those who, whilst others worshipped God by stealth, bravely dared all persecution by openly assembling to worship God as their consciences dictated. So he thought within himself, that "if the Lord Jesus Christ had a visible Church on earth these must be they." But all this merely cleared the ground for the final and decisive proof, without which he would never have made a Friend. Feeling his judgment satisfied by these tests, he yielded his heart to the influence of the truth, and he experienced a peace which insults and sufferings could not disturb, and gained an experimental acquaintance with God that satisfied the cravings of his soul. He became distinguished for his solemn fervour in prayer, his deep piety and uncomplaining meekness in ill-usage--the latter, "a virtue," says one of his descendants, "he was before very much unacquainted with." "One of his relations, upon an occasion of uncommon rudeness, lamenting that he should be now treated so differently from what formerly he had been, he answered, that he found more satisfaction as well as honour in being thus insulted for his religious principles, than when, some years before, it was usual for the magistrates as he passed through Aberdeen, to meet him several miles, and conduct him to a public entertainment in their town-house, and then convey him so far out again, in order to gain his favour." This noble testimony is the subject of one of Whittier's most spirited ballads. The old soldier lived to a ripe old age, his son only surviving him four years.