John Chrysostom

What then saith Christ? "Because it is given unto you," so He speaks, "to know the mysteries of the Kingdom of Heaven, but to them it is not given." But this He said, not bringing in necessity, or any allotment made causelessly and at random, but implying them to be the authors of all their own evils, and wishing to represent that the thing is a gift, and a grace bestowed from above. It by no means follows, however, because it is a gift, that therefore free will is taken away; and this is evident from what comes after. …

Homily on the Gospel of Matthew 45 ↗

Thomas Aquinas

Likewise, here it should be considered that what pertains to the salvation of men should always be done. Hence the response follows: who answering said to them. And first the ordinance of God is set down; secondly, a certain reason is assigned. He says, therefore I say that I speak in parables, because to you it is given to know the mysteries of the kingdom of heaven, but to them it is not given: in which words three things are set down. First, that some are understanding and some are not. …

Commentary on Matthew ↗

Remigius of Rheims

To you, I say, who adhere to Me, and believe in Me. By the mystery of the kingdom of heaven, He intends the Gospel doctrine. To them, that is, to them that are without, and who would not believe on Him, the Scribes namely and Pharisees, and to the rest who continue in unbelief, it is not given. Let us then, with the disciples, come unto the Lord with a pure heart, that He may think us worthy to interpret to us the evangelic teaching; according to that, They who draw near to his feet, shall receive of his doctrine. (Deut. 33:3)

Catena Aurea by Aquinas ↗