13 These men, too, dare to say that they are wont to suffer persecution from catholic kings, or from catholic princes. What persecution do they bear? Affliction of body: yet if at times they have suffered, and how they suffered, let themselves know, and settle it with their consciences; still they suffered only affliction of body: the persecution which they cause is more grievous. Beware when Ishmael wishes to play with Isaac, when he fawns on you, when he offers another baptism: answer him, I have baptism already.
For if this baptism is true, he who would give you another would be mocking you. Beware of the persecution of the soul. For though the party of Donatus has at times suffered somewhat at the hands of catholic princes, it was a bodily suffering, not the suffering of spiritual deception. Hear and see in the very facts of Old Testament history all the signs and indications of things to come. Sarah is found to have afflicted her maid Hagar: Sarah is free. After her maid began to be proud, Sarah complained to Abraham, and said, “Cast out the bond woman;” she has lifted her neck against me.
His wife complains of Abraham, as if it were his doing. But Abraham, who was not bound to the maid by lust, but by the duty of begetting children, inasmuch as Sarah had given her to him to have offspring by her, says to her: “Behold, she is your handmaid; do unto her as you will.” And Sarah grievously afflicted her, and she fled from her face. See, the free woman afflicted the bond woman, and the apostle does not call that a persecution; the slave plays with his master, and he calls it persecution: this afflicting is not called persecution; that playing is.
How does it appear to you, brethren? Do you not understand what is signified? Thus, then, when God wills to stir up powers against heretics, against schismatics, against those that scatter the Church, that blow on Christ as if they abhorred Him, that blaspheme baptism, let them not wonder; because God stirs them up, that Hagar may be beaten by Sarah. Let Hagar know herself, and yield her neck: for when, after being humiliated, she departed from her mistress, an angel met her, and said to her, “What is the matter with you, Hagar, Sarah's handmaid?”
When she complained of her mistress, what did she hear from the angel? “Return to your mistress.” It is for this that she is afflicted, that she may return; and would that she may return, for her offspring, just like the sons of Jacob, will obtain the inheritance with their brethren.
Source: Tractates on the Gospel of John (New Advent)