His Essay on the Connexion between the Doctrine of Justification by the Imputed Righteousness of Christ and Holiness of Life (1756) was his principal theological work.
The holiness of Israel centres in the sanctuary, and round the sanctuary stand the priests, who alone can approach the most holy things without profanation, and who are the guardians of Israel's sanctity, partly by protecting the one meeting-place of God and man from profane contact, and partly as the mediators of the continual atoning rites by which breaches of holiness are expiated.
But a distinction of grades of holiness gained by ascetic life has never been entirely foreign to the Eastern mind, and in the popular faith of Mahommedan peoples something very like priesthood has crept in by this channel.
For where holiness is associated with ascetic practices the masses can never attain to a perfect life, and naturally tend to lean on the professors of special sanctity as tke mediators of their religious welfare.
Contributing to the same result was the emphasis upon the necessity of personal purity or holiness, which Paul's contrast between flesh and spirit had promoted, and which early took the supreme place given by Christ to love and service.