The cunning teaching
6 “Be careful,” Jesus said to them. “Be on your guard against the yeast of the Pharisees and Sadducees.”
7 They discussed this among themselves and said, “It is because we didn’t bring any bread.”
8 Aware of their discussion, Jesus asked, “You of little faith, why are you talking among yourselves about having no bread? 9 Do you still not understand? Don’t you remember the five loaves for the five thousand, and how many basketfuls you gathered? 10 Or the seven loaves for the four thousand, and how many basketfuls you gathered? 11 How is it you don’t understand that I was not talking to you about bread? But be on your guard against the yeast of the Pharisees and Sadducees.” 12 Then they understood that he was not telling them to guard against the yeast used in bread, but against the teaching of the Pharisees and Sadducees.
The guard of the mind
Saint Simeon the New Theologian, Catechesis, Writings II, Catechesis 12, in Filocalica, Deisis, p 163-164
`Brothers and fathers being always helpless with my soul and body because of an idle and reckless will I wished I would have done and search only my own affairs until my bad parts would be defeated and subdued to the good thought to delight entirely of the peace of the Spirit being freed of the trouble of the earthly thought and entering in the port of our blessed rest. But as I was elected by you as a head of your holy body it is a need for me to urge your love because your salvation comforts me by the fact that although I am helpless with my soul at least you will find your salvation by the help of the prayers of my father and your father. (John 20, 17).
Therefore not being able to open my mouth I could only write this speech and draw your attention beseeching you as being true servants of Christ and fond of your brothers to pray for my wretchedness to be able to find salvation with you and walk on the path of God`s commandments and live with you, my beloved brothers. Thus I implore and ask you in the name of Jesus Christ to meditate at yourself and think, everyone of you, about wisdom and about what you should think (Romans 12, 3), without looking at my reckless and careless life but walk on the traces of our Lord and Saviour Jesus Christ to Whom we have to give answer as to a just and truthful judge. Allow me this praise (II Corinthians 11, 1) as I, being drawn to the abyss of hell, cause my idleness, took you out from the trap, with a great cry and although I have to cry a lot for my idleness, it will be enough for me if I see you flying to heavens over the traps of the devil.
Therefore keep without fault all the commandments of God, my beloved and escape as some antelopes from traps and as a bird from its lath (Proverbs 6, 5; Psalms 123, 7).
The first commandment is to love God from all our heart and love one another (Matthew 22, 37-39), as God loved the world (John 3, 16).”