The concept of being unreasonable is defined as: "not agreeable to reason, exceeding the bounds of reason, immoderate, not influenced by reason" (Chambers). All of these definitions render a person unable to reason. There is also the possibility of some problem with brain function that may not allow a person to think clearly, but I will not address that. Not being agreeable to reason is often driven by some inner flaw in the person such as that which lies in the heart (ego, vanity, pride, fear, hate, biases and prejudice). Many people are lacking in self-control, so their lives and opportunities are often driven by explosive tempers, lack of self-control, lust and passion, anxiety and doubt. All of these affect our ability to think clearly and logically. We might also differ at times with defining what 'to reason' is.
Chambers dictionary defines 'to reason' as: "the mind's power of drawing conclusions and determining right and truth". To exercise this faculty: "to deduce inferences from premises; to argue; to debate; to examine, to discuss; to debate; to think out; to set forth logically; to bring by reasoning". Listening to reason is: "to take heed of, the reasonable explanation, course of action." Pure reason is absolutely independent of experience. Putting all of these points together it is obvious that deep inner flaws can make it impossible for a person to reason about things that may be logical and true. That inability makes a person unreasonable and often unreachable. When a person is not governed by reason, he will not listen to truth or logic and may put up barriers to communication in order to protect the inner turmoil he may be feeling. All of us have been brought up in conditions that are not perfect because we have imperfect parents, live in an imperfect society, are impacted by imperfect knowledge and lack the control of the self which makes is possible for us to reason well. To one extent or another, all humans are affected in this way. The good news is that we do not have to remain this way, we can learn and change. We are able to overcome deep inner hurts or convictions and remove the barriers that prevent us from hearing truth and logic. There are many examples of people who have overcome incredible barriers in their lives to be wonderful, balanced, free thinking people who can reason well and who are not unreasonable. They may have been that way for part of their lives, but have overcome.
The Bible boldly states: "The fool has said in his heart, 'There is no God'" (Psalm 14:1-3,53:1-3). Both of these Psalms explain that people are corrupt, have done abominable works and are not good. God looks down and sees that none are doing good. That does not mean there is not a mixture of good and evil in a person, but the consistent ability to choose to do good and know good fails. The reasons have been mentioned above and to add to that, we are living in a world strongly influenced by the force of evil. Satan is the god of this world who has blinded mankind (2 Cor. 4:4).
We live in a world in which we are surrounded with thousands upon thousands of perfectly formed and functioning living things from plants to animals, birds, fish and insects. All of them are so incredible that only a fool would say they have come to be by some accident of nature. There is a Creator, a brilliant mind that has created all the wonders we see. He has done that with the purpose of developing spiritual children who will live with Him and reign in this universe forever (Mal. 2:15, Rom. 8:16-19). God has given mankind the freedom to think, learn, determine and choose. He has laid before them in all clarity, that which is good versus evil, holy versus profane and right versus wrong and then encourages and demands that we think and make the right choice (Deut. 30:15). We are created so that we need about 20 years in which to grow to maturity. It is determined that the brain continues to develop to age 25. We need to learn how to reason well because we are not born with this gift of clear thinking. As we grow, our parents, the society in which we live, experience and commonsense ought to teach us to stop and think - that is to reason. Gather all the information we can about a subject and then make the good and proper decision about the path we will take. We need healthy brains and minds to think this way.
God inspired His prophet Isaiah to express His anger and frustration with mankind. He said the people He chose did not consider (Isa. 1:3). They did not complete the steps that are needed in order to think clearly. They were misled by all the errors within themselves. Isaiah wrote that we are to learn to make ourselves clean, put away evil and do good - then God said: "Come now, and let us reason together." (Isa. 1:16-18). There are many lessons humans need to learn before they can reason at a high level, but it is vital that they do learn. The rewards are great and the punishment for failure is painful. Jesus was busy teaching His followers to reason clearly. They needed to carefully consider what was happening in order to understand all the events. In one instance they were reflecting on Jesus' words in a limited way and Jesus had to address that (Matt. 16:1,6-12). They needed to learn that Jesus spoke about leavening of the Pharisees and Sadducees rather than the physical loaf of bread. One of the biggest problems the disciples wrestled with was the desire each seemed to have to be called the greatest (Luke 9:46-48). That problem persisted until the death and resurrection of Jesus. We often have deeply embedded flaws that hamper our ability to reason or to be reasonable.
God follows the reasoning that goes on in our hearts and wants to help us think clearly. That is why the wonderful book we call the Bible was written and so carefully preserved for the last 4000 or so years. There is no other book like this on earth. But knowledge, understanding and developing a large bank of proper and correct information does not come automatically. It takes time - years and decades to grow in this area for most people on earth. Most people are steeped in various religious beliefs or some inner driving belief that blocks them from seeing the light that Jesus brought. Sadly enough, men love the darkness they have grown up in because change is not easy (John 3:19).
The scientific method which was only stated a couple of hundred years ago states that we: "Make an observation, Ask a question, Formulate a hypothesis, Make a prediction. Test your prediction (experiment). Repeat your experiment. Revise your hypothesis if needed. Share your findings." That seems simple enough, but it is an orderly approach that requires patience, self-control and right thinking. It requires the putting aside of inner biases, prejudices and all wrong thoughts. We humans have shown that we can do this in the physical realm (though we still wrestle with hindrances), but we find ourselves almost helpless to reason well in the spiritual realm. The spiritual realm lasts for eternity, so it is much more important.
Peter was a disciple who had to overcome prejudices, biases, temper, fear and that which makes him and us human. He did overcome to a great degree and recorded the steps we must take. Peter said that if we want to reach the realm of the divine, we need to be diligent, knowledgeable, self-controlled, persevere and love one another (2 Pet. 1:4-8,11). He showed that it can be done. God would not command us to do the impossible. He has made eternal life in His family possible - the outcome for each of us only awaits our actions. Stop and think, examine yourself and take the steps needed to reason well.