I. Abstinence must include discipline of the soul as well as of the body
There is nothing, dearly-beloved, in which the Divine Providence does not assist the devotions of the faithful. For the very elements of the world also minister to the exercise of mind and body in holiness, seeing that the distinctly varied revolution of days and months opens for us the different pages of the commands, and thus the seasons also in some sense speak to us of that which the sacred institutions enjoin. And hence, since the year's course has brought back the seventh month to us, I feel certain that your minds are spiritually aroused to keep the solemn fast; since you have learned by experience how well this preparation purifies both the outer and the inner parts of men, so that by abstaining from the lawful, resistance becomes easier to the unlawful.
But do not limit your plan of abstinence, dearly-beloved, to the mortifying of the body, or to the lessening of food alone. For the greater advantages of this virtue belong to that chastity of the soul, which not only crushes the lusts of the flesh, but also despises the vanities of worldly wisdom, as the Apostle says, “take heed that no one deceive you through philosophy and empty deceit, according to the tradition of men.”
Source: Sermons (New Advent)