The principal word translated "hear" in the NT is akouo. When we use the word "hear" in the English language, to what do we often refer? The word is often understood as the physical sense used to experience sound. However, it is infrequently used to communicate an idea dealing with what happens to the sound heard within the mind of the hearer. Modern English vocabulary contains other words used to express understanding. However, NT usage of the word "hear" may refer to either the physical sense or the understanding of the words spoken. Which is which depends upon the way the word is used in the Greek. For example, Paul tells us in Acts 9:7 that the men which journeyed with him on the Damascus road "stood speechless, hearing a voice, but seeing no man." However, Luke's recording of the same event in Acts 22:9 states that "they heard not the voice of him that spake to me." ("they" referring to the ones who were with him on the Damascus road). Isn't this a clear contradiction within the scriptures? How could they have heard the voice in 9:7, but not hear the voice in 22:9? I've provided a link to Vine's dictionary to fully explain the differences, but in essence the key difference is the case of the noun used in the Greek text. In 9:7 the case indicates a sensory process (i.e. hearing the sound), but in 22:9 the case indicates perception (i.e. understanding the sound heard). So, we learn from these two verses that the men with Paul heard a voice with their physical sense of hearing, but their mind failed to understand the words being spoken by the voice.
Let's look at another example. We've considered John 9:27 in an earlier study. Briefly, we see the man blind from birth that tells the Pharisees how he regained his sight. When they asked a second time how he regained his sight, he tells them, "I have told you already, and ye did not hear: wherefore would ye hear it again?" Clearly he is referring to their unwillingness to believe the sounds they heard through the words spoken by the formerly blind man. In a similar vein, Jesus tells the Pharisees in John 8:43 and 44 that they did not understand His speech because "ye cannot hear My word." Why was it not possible for them to hear His word? He tells us in verse 44: They were of their father, the devil! (For those of you who were wondering, the Greek word used in verse 43 for "cannot" is ou--the word indicating an absolute negative. See our study on Baptism, under the section dealing with Baptism for the Dead for further information). So Jesus tells the Pharisees that they were absolutely unable to "hear" His word, since they were children of the devil. Was there something wrong with their ears? No! There was something wrong with their hearts! Being children of the devil they were incapable of understanding His words and applying them to their lives. Does the 8th chapter of John seem familiar? If you've gone through our study on "Who is a Christian" it will. Remember how we spent quite a bit of time dealing with Jesus' statement that "If ye continue in My word, then are ye my disciples indeed;"? This is recorded in John 8:31. John 8:43 is contained within the same discourse between Jesus and the Pharisees! What did we conclude any word spoken by man as religious doctrine but which differs from Jesus' word constitutes? We showed how such a "word" is born of the devil, and practicing such worship is in vain. How do people today differ from the Pharisees of old in this regard? They don't! Jesus summarizes this in verse 47 of the same chapter: "He that is of God heareth God's words: ye therefore hear them not, because ye are not of God." Jesus told us in verse 43 that he is not speaking of the physical sense of hearing. So, in verse 47, those who are of God understand, believe, and apply His word to their lives (He that is of God heareth God's words). Any one who fails to do any one of these three is not of God. Do we read of a third option in these verses? No! Jesus tells us that we are either of God, or of the devil. There is no in-between mentioned by Jesus in this discourse. If we understand, believe, and apply His words to our lives, we are of God. If we believe the words of man rather than those of Jesus, we are not of God. If we are not of God, we are of the devil. If we are of the devil, what is our eternal fate? Jesus tells us in Matthew 25:41: we will spend eternity in everlasting fire, prepared for the devil and his angels.
Jesus shows us again in Matthew 13:13 how we can hear words, but not understand the meaning of the words spoken. The disciples asked Jesus why he spoke in parables. He replied that he did so "because they seeing see not; and hearing they hear not, neither do they understand." Were these people capable of hearing the words spoken by Jesus (that is, was their sense of hearing intact)? Yes. He said that "hearing they hear not." If their physical sense of hearing had been impaired Jesus would not have used such a phrase. However, their understanding of the words He spoke was lacking. For this reason He spoke to them in parables. Let's continue through the next few verses. Jesus continues His thoughts on hearing but not understanding. Verse 14: "By hearing ye shall hear, and not understand;", verse 15: "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." Clearly their problem was one of the heart, not of the physical sense of hearing.