Why did Jesus tell the parables of the wheat and the weeds, the mustard seed, and the yeast? Leo XIV answers
Address on the Occasion of the Angelus Prayer on Sunday, July 19, 2026
2 months ago
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Investigate Catholic teachings on Jesus' parables of wheat, weeds, mustard, and yeast
These three parables—wheat and weeds (tares), mustard seed, and yeast/leaven—form a coherent Catholic picture of how Christ’s kingdom grows in history: evil is real but will not be removed prematurely, the Gospel grows from small beginnings into great life, and the truth works secretly and progressively until it permeates everything.
Jesus compares the kingdom to a field where good seed is sown, but an enemy oversows weeds among the wheat while people are “asleep.”
When the plants grow, the servants notice the weeds and ask whether they should pull them out.
Jesus’ response is decisive: “No; for in gathering the weeds you would uproot the wheat along with them.”
Thomas Aquinas explains that Christ does not want the weeds collected yet because the Lord is dealing “patiently… not willing that any should perish.”
Aquinas then gives four reasons why evil men should not be wiped out for the sake of good men:
In short: the moral and spiritual harm of premature separation can outweigh the visible “benefit” of quick removal.
Jesus states: “Let both of them grow together until the harvest.”
Aquinas glosses that this sparing is “only for a time.”
He also addresses an objection: why not purge evil immediately? Aquinas cites patristic reasoning (Chrysostom and Augustine) that violence can produce conversions but also often produces further evils—so removal is limited by the risk to salvation and to the Gospel’s spread.
Aquinas’ key interpretive claim is that the “harvest” points to the time of final judgment, with two “harvests” (one in the Church now, one “in the heavenly”).
At harvest time, reapers gather the weeds first, bind them into bundles, and burn them; then the wheat is gathered into the barn.
Aquinas interprets this as a final separation:
Aquinas reads the weeds as wicked children—especially heretics—because they resemble wheat while corrupting the field.
He emphasizes that these evildoers are not originally planted as weeds but “put on the appearance” of good men.
Jesus says: the kingdom of heaven is like a mustard seed, the smallest seed, but when grown it becomes “the greatest of shrubs,” even a tree where birds nest.
Aquinas emphasizes the logic of the parable: Jesus is answering a fear that the Gospel cannot progress if impeded—so He uses growth imagery.
The mustard seed illustrates both:
In the Catena Aurea (Aquinas’ compiled patristic tradition), Jerome explains that the mustard seed can signify the preaching of the Gospel and the knowledge of Scripture leading to life.
Other patristic readings also interpret Christ himself as the mustard seed:
So, Catholic tradition can read the parable both christologically (Christ is the living source) and ecclesially/evangelically (the Gospel preached grows in history).
Aquinas’ Catena indicates birds nesting in the branches signify refuge/rest. For example:
Jesus says the kingdom is like yeast that a woman mixes into three measures of flour until all is leavened.
Aquinas stresses the “marvelous” feature: the kingdom grows from a hidden seed; likewise leaven is concealed yet eventually affects the whole.
He also warns that in Scripture leaven can sometimes symbolize evil corruption, but in this parable it connotes good because it enlarges with power and produces transformation.
Aquinas presents several “what is signified by leaven” readings:
The Catena Aurea likewise explains that leaven changes the whole into its own kind, and it interprets “three measures” as abundance (a finite number for an indefinite greatness).
Aquinas interprets the phrase “until the whole was leavened” as completion: the leaven works “until all were converted to God.”
The Catholic Encyclopedia warns against demanding scientific precision from popular images (like “least of seeds”), and it points out that the focus is on the kingdom’s humble beginnings and extraordinary development.
It also suggests that these parables are “cognate” and belong together: mustard seed and leaven both speak to a mystery of regeneration and growth over time.
Taken together, the parables teach that Christ’s kingdom is patient with mixed realities, powerfully expansive from small starts, and mysteriously transformative through hidden internal action, with a final and definitive separation at the harvest.