The subject of this Sunday's Gospel is, precisely, the Kingdom of Heaven. “Heaven” should not be understood only in the sense that it towers above us, because this infinite space also takes the form of human interiority. Jesus compares the Kingdom of Heaven to a field of wheat to enable us to understand that something small and hidden has been sown within us which, nevertheless, has an irrepressible vital force. In spite of all obstacles, the seed will develop and the fruit will ripen. This fruit will only be good if the terrain of life is cultivated in accordance with the divine will.
For this reason in the Parable of the Weeds [tares] among the good Wheat (Mt 13:24-30). Jesus warns us that, after the owner had scattered the seed, “while men were sleeping, his enemy” intervened and sowed weeds among the wheat. This means that we must be ready to preserve the grace received from the day of our Baptism, continuing to nourish faith in the Lord that prevents evil from taking root. St Augustine commenting on the parable noted “many are at first tares but then become good grain”, and he added: “if these, when they are wicked, are not endured with patience they would not attain their praiseworthy transformation” (Quaest. septend. in Ev. sec. Matth., 12, 4: PL 35, 1371).
[Pope Benedict, Angelus 17 July 2011]