Inevitably within a religious philosophy taking the Old Testament as its basic text ethics plays an important part, and since the Old Testament was believed by Philo to be inspired by the one true God its ethics and those derived from it were believed to be superior to all others.

For one who was a subtle philosophical thinker and whose religion contained a profound and extensive element of mysticism – or at least possessed distinct mystical traits – Philo's attitude, because it was so thoroughly Jewish, was intensely practical and firmly incorporated the belief that its adherents must be actively involved in the life of mankind and society. As Philo himself asks, ‘what use is the flute-player, however fine a performer he may be, if he remains quiet… or the harpist if he does not use his harp or in general any craftsman if he does not exercise his craft?’ So ‘motion … is the proper condition for the good … No knowledge is profitable to the possessors through the mere theory if it is not combined with practice’ (Congr. 45–6). Philo, then, was not a religious thinker concerned only with theoretical matters. One of the most important means of acquiring the Good is ‘through practice and not through teaching’, for ‘the practiser must be the imitator of a life’. Virtue may be achieved through teaching by the learner who ‘listens to a voice and to words’ (ibid. 69–70), but all true virtue is ‘perfected through practice’ (ibid. 35). Philo could write (Cher. 102) of the ‘virtues and the good actions that follow them’.