Why Jackson should have preferred the Presbyterian denomination to all others we are nowhere told. But whatever his reasons may have been, he was a most zealous and hardworking member of his church. He was not content with perfunctory attendances at the services. He became a deacon, and a large portion of his leisure time was devoted to the work which thus devolved on him. His duties were to collect alms and to distribute to the destitute, and nothing was permitted to interfere with their exact performance. He was exceedingly charitable himself—one tenth of his income was laid aside for the church, and he gave freely to all causes of benevolence and public enterprise. At the church meetings, whether for business or prayer, he was a regular attendant, and between himself and his pastor existed the most confidential relations. Nor did he consider that this was all that was demanded of him. In Lexington, as in other Southern towns, there were many poor negroes, and the condition of these ignorant and helpless creatures, especially of the children, excited his compassion. Out of his own means he established a Sunday school, in which he and his wife were the principal teachers. His friends were asked to send their slaves, and the experiment was successful. The benches were always crowded, and the rows of black, bright-eyed faces were a source of as much pride to him as the martial appearance of the cadet battalion.
Jackson’s religion entered into every action of his life. No duty, however trivial, was begun without asking a blessing, or ended without returning thanks. “He had long cultivated,” he said, “the habit of connecting the most trivial and customary acts of life with a silent prayer.” He took the Bible as his guide, and it is possible that his literal interpretation of its precepts caused many to regard him as a fanatic. His observance of the Sabbath was hardly in accordance with ordinary usage. He never read a letter on that day, nor posted one; he believed that the Government in carrying the mails were violating a divine law, and he considered the suppression of such traffic one of the most important duties of the legislature. Such opinions were uncommon, even amongst the Presbyterians, and his rigid respect for truth served to strengthen the impression that he was morbidly scrupulous. If he unintentionally made a misstatement—even about some trifling matter—as soon as he discovered his mistake he would lose no time and spare no trouble in hastening to correct it. “Why, in the name of reason,” he was asked, “do you walk a mile in the rain for a perfectly unimportant thing?” “Simply because I have discovered that it was a misstatement, and I could not sleep comfortably unless I put it right.”