Commenting on the parable of the dragnet (Matthew 13:47-50), Trench writes:
...the Lord did not contemplate His visible Church as a communion in which there should be no intermixture of evil; but as there was a Ham in the ark, and a Judas among the twelve, so there should be a Babylon even within the bosom of the spiritual Israel; Esau shall contend with Jacob even in the Church's womb... This fact does not justify self-willed departure from the fellowship of the Church, an impatient leaping over , or breaking through, the nets, as it is often called; but the Lord's separation is patiently to be waited for.... (R. C. Trench, Notes on the Parables of Our Lord)
Following Trench's footnote pointing to Augustine's exposition of Psalm 126:3 (127:3), "the fruit of the womb is a reward," Augustine...
But to whose womb is the Psalm referring? That of the Church. Rebecca was another type of the Church when twins struggled within her like two contending peoples. One mother held together within her body two brothers already at variance even before their birth. They battered their mother's belly with their antenatal wrangling. She moaned at the violence she was enduring, but when the time came to bring them forth she marked the difference between the twins who had made her pregnancy so difficult. The same is true today, brothers and sisters, as long as the Church's lot is to moan with pain, as long as she is in labor with her children, for within her are both good and bad people. (Augustine on Psalm 126:3 [127:3])