Jesus explains why it is that He teaches the people in parables. In keeping with many of the pictures of the Old Testament, such as the fiery pillar and the types and shadows of the ceremonial law, these things were designed to shed light and understanding on the people of God, whilst being incomprehensible to the lost.
It is the sovereign grace of God, acting according to His good pleasure alone, that enables those born blind and deaf through sin to see and hear the beauty of Christ in the Gospel and to come to Him.
We are encouraged to see here a great blessing and privilege from God to His people - to have been entrusted with the secrets of the mystery of the kingdom of heaven and to be able to understand and profit from these things. We should rejoice in this goodness of our God, which is entirely of His grace and owes nothing to us at all.
On the other hand, if we are still ever hearing God’s word but never understanding it and if we are ever seeing but never perceiving spiritual things, we need to see that we are not the children of God. We should heed the warning of this passage and come to Christ at once for salvation and the accompanying blessings of those admitted to the household of God.