Clement of Alexandria

At times our Savior spoke the Word to the apostles by means of mysterious sayings. For prophecy says of him: "He will open his mouth in parables, and will declare things kept secret from the foundation of the world." … The efficacy of the Word itself, being strong and powerful, gradually draws into itself secretly and invisibly everyone who receives it.

The Stromata Book 5 ↗

Jerome

So that what was said through the prophet might be fulfilled, saying: I will open my mouth in parables; I will utter things hidden since the foundation of the world. This testimony is taken from the seventy-seventh psalm (Verse 2). It is read in some codices, and a diligent reader may perhaps find the same thing in the place where we have put it, and the Vulgate edition has: So that what was said through the prophet might be fulfilled, written there, through the prophet Isaiah, saying. …

Commentary on Matthew ↗

Thomas Aquinas

That it might be fulfilled which was spoken by the prophet saying: I will open my mouth in parables. In two ways the Lord spoke to the human race. First, in the prophets; secondly, in himself; Isa 52:6: behold, I who spoke, behold I am here. In both cases he spoke parabolically: in the prophets in many ways, and through himself likewise: for what was done in the prophets was a sign of what was to be done through Christ; hence he says, I, the Lord, who opened the mouth of the prophets in parables, will open it in myself. …

Commentary on Matthew ↗