The secrets of the kingdom of God have been given for you to know, but to the rest it is in parables, so thatLooking they may not see,
and hearing they may not understand.
Notice that this understanding is not something that the disciples acquired for themselves; it was a gift. Notice also verse 17 of Matt 13:
Many prophets and righteous people longed to see the things you see yet didn't see them; to hear the things you hear yet didn't hear them.
God may have called you to be a prophet, or you may be a very righteous person, but that does not automatically qualify you to have understanding. Understanding is not something you acquire for yourself; it's something that is given to you from God.
We see the same sort of God-given understanding later (Matt. 16:17), when Peter pronounced Jesus as the Messiah:
And Jesus responded, "Simon son of Jonah, you are blessed because flesh and blood did not reveal this to you, but My Father in heaven."
Paul sums up this idea in 1 Corinthians 2:10ff, emphasizing that without the Spirit of God dwelling in us, we will fail to understand the things of God:
Now God has revealed them to us by the Spirit, for the Spirit searches everything, even the deep things of God. ... Now we have not received the spirit of the world, but the Spirit who is from God, in order to know what has been freely given to us by God. But the natural man does not welcome what comes from God's Spirit, because it is foolishness to him; he is not able to know it since it is evaluated spiritually. The spiritual person, however, can evaluate everything.... For:who has known the Lord's mind,But we have the mind of Christ.
that he may instruct Him?
The take-home message, for me at least, is that we should recognize that the Spirit does indeed "magically" work directly on our minds, even if we're not aware of it. To claim otherwise is a form of quenching the Spirit, and is quite unBiblical.