24 Truly, truly, I say to you, unless a grain of wheat falls into the earth and dies, it remains alone; but if it dies, it bears much fruit. 25 He who loves his life loses it, and he who hates his life in this world will keep it for eternal life. 26 If any one serves me, he must follow me; and where I am, there shall my servant be also; if any one serves me, the Father will honor him. (John 12.24-26)
33 He told them another parable. “The kingdom of heaven is like leaven which a woman took and hid in three measures of flour, till it was all leavened.” (Matthew 13.33)
In the Gospel we read: “Unless the grain of wheat falls into the ground and dies, it remains but a single grain ; but if it dies it bears much fruit” (John 12.24). Our Lord Jesus is the grain of wheat but he is also the yeast… When he came, a man and alone, into the world, the Lord Jesus gave everyone the opportunity to become what he is himself. Anyone who is united to the yeast that is Christ also becomes yeast, useful to the self and of value to all. That person will be saved and will save others.
Before it is mixed into a bowl of flour, the yeast is beaten, crushed, and crumbed; it is completely dissolved. But it is then that, in one and the same fermentation, it take on the same appearance as the numerous dispersed grains of flour. It brings together into a solid lump a substance that, of itself, used to be as inconsistent as dust. In fact it creates a serviceable dough out of what seemed to be nothing but a scattering of dust.
Thus the Lord Jesus Christ, yeast of the whole world, has been crushed by much suffering, pierced and destroyed. And his sap – that is to say, his precious blood – was poured out for us so as to solidify all humankind that was scattered by becoming mingled with them,. We who used to be like a people of flour, see how we are now brought together as by yeast. We who were miserably lying all over the earth, scattered and crushed: see how we are reunited with Christ’s body thanks to the power of his Passion. —Saint Maximus of Turin (?-c.420), Homily 111 ; CC Sermon 25, p.97 ; PL 57, 511