Christ told His friends, that is, His disciples, to beware of the leaven of the Pharisees and scribes, meaning by leaven their false pretence. For hypocrisy is a thing hateful to God, and abominated by man, bringing no reward, and utterly useless for the salvation of the soul, or rather the cause of its perdition. Though sometimes it may escape detection for a little, yet before long it is sure to be laid bare and bring disgrace upon them, like ill-featured women, when they are stripped of that external embellishment which they had produced by artificial means. Hypocrisy, therefore, is a thing foreign to the character of the saints. That it is impossible for those things that are done and said by us to escape the eye of the Deity, He showed by saying: “There is nothing covered that shall not be revealed; neither hid that shall not be known.” For all our words and deeds shall be revealed at the day of judgment.
The enemy of our salvation especially strives to draw our heart and mind away from God when we are about to serve Him, and endeavors to adulterously attach our heart to something irrelevant. Be always, every moment, with God, especially when you pray to Him. If you are inconstant, you will fall away from life, and will cast yourself into sorrow and straitness.
No, the God of love and peace and complete sacrifice does not care to live in the midst of bustling and ado to please oneself, even if this is carried on perhaps under some kind of pretence. There is one way to make a test: if your peace of mind is troubled, if you become dejected or perhaps a little angry if for some reason you have to give up performing the good deed you had planned, then you know that the spring was muddy.
St. Paul says: 'The person engaged in spiritual warfare exercises self control in all things' (I Cor. 9:25). Aware of all that is said in divine Scripture, let us lead our life with self-control, especially in regard to food.
No virtue makes flesh-bound man so like a spiritual angel as does self-restraint, for it enables those still living on earth to become, as the Apostle says, 'citizens of heaven' (cf. Phil. 3:20).
Lack of self-control is actually an evil both ancient and modern, though it did not precede its antidote, fasting. By means of our Forefathers' self-indulgence in paradise and their contempt for the fast already in existance there, death entered the world. Sin reigned and brought in the condemnation of our nature from Adam until Christ.