Matthew 13:12-15 KJV For whosoever hath, to him shall be given, and he shall have more abundance: but whosoever hath not, from him shall be taken away even that he hath.  Therefore speak I to them in parables: because they seeing see not; and hearing they hear not, neither do they understand.  And in them is fulfilled the prophecy of Esaias, which saith, By hearing ye shall hear, and shall not understand; and seeing ye shall see, and shall not perceive:  For this people’s heart is waxed gross, and their ears are dull of hearing, and their eyes they have closed; lest at any time they should see with their eyes, and hear with their ears, and should understand with their heart, and should be converted, and I should heal them.
I have often wondered what makes some people deaf to all or even part of the word of God. I have conjectured that it requires increased faith to increase knowledge. Being baptized, one is introduced to the family of God. Are some deaf to the truth because they have not yet been baptized? Perhaps being part of the family of God clears ears and open eyes. Honestly though, one must have a certain amount of faith and understanding just to be baptized. The baptizee must repent of their sins and know Jesus is the Christ.
From my own experience it seems that there are levels of truth that people can accept. For example, the Church of Christ can accept nine of the Ten Commandments, but they can’t accept the Sabbath law. They can accept miracles then, but not now, despite the promises in James.
Jesus said in John 8:47 KJV, He that is of God heareth God’s words: ye therefore hear them not, because ye are not of God.
What then if they hear some of God’s word, but not all of it. It is a dangerous and precarious position. Indeed, even what you have may be taken away. I believe this is the cause of much of the strange doctrine out there. Rather than growing in faith and understanding these once true believers are drawn aside to half truths and whims of fancy rather than the God given knowledge they once possessed.
Romans 10:17 KJV says, So then faith cometh by hearing, and hearing by the word of God.
If you hear the word of God, take it to heart. Pray for faith. Pray also for wisdom and understanding. Be careful both to hear and do the Word, lest what you have is taken away.