Early American concepts of spiritual friendship became increasing important in the wake of religious revivalism and denominational growth during the eighteenth and nineteenth centuries. White, middle class Protestants forged intimate relationships based on common religious beliefs, which developed into spiritual friendship. They exhibited friendliness by nurturing it in themselves and others and by spreading the love of Christ. Yet spiritual friends were to be selective; believers were to form friendships only with likeminded Protestants-both across classes and between genders-to keep each other on the path to righteousness. Spiritual friendship was not merely a social practice; it was a Christian duty that created a bond among true believers through Christian fellowship. Church meetings, household gatherings, leisure activity, conversation, and letter writing maintained spiritual friendship. The intimacy and depth of spiritual friendship generated by these wholesome pursuits resulted in sympathy as well as intimacy. The benefits of spiritual friendship included devoted companionship and intense interaction; through mutual feelings and shared beliefs, spiritual friendship became "this union of the soul." Spiritual friendship contributed to the development of modern notions of friendship, which were based primarily on emotional closeness rather than geographic proximity, familial connection, or class status.