"And he answered, 'You shall love the Lord your God with all your heart and with all your soul and with all your strength and with all your mind, and your neighbor as yourself.'" (Luke 10.27 ESV)
In Christianity we affirm that the gospel is revealed to us within our souls by the Holy Spirit; this is revelation. However, what can we learn by reason, by our thinking things through to logical conclusions? In short, how can we know God by reason?
In his Sermons, # 70, "The Case of Reason Impartially Considered", Wesley attempts to strike a balance between under-valuing reason and over-valuing it.
Wesley begins by defining reason:
"First, then, reason is sometimes taken for argument. So, 'Give me a reason for your assertion.' So in Isaiah: 'Bring forth your strong reasons;' that is, your strong arguments. We use the word nearly in the same sense, when we say, 'He has good reasons for what he does.' It seems here to mean, He has sufficient motives; such as ought to influence a wise man."
"In another acceptation of the word, reason is much the same with understanding. It means a faculty of the human soul; that faculty which exerts itself in three ways;---by simple apprehension, by judgement, and by discourse. Simple apprehension is barely conceiving a thing in the mind; the first and most simple act of understanding. Judgment is the determining that the things before conceived either agree with or differ from each other. Discourse, strictly speaking, is the motion or progress of the mind from one judgment to another. The faculty of the soul which includes these three operations I here mean by the term reason."
John Wesley valued the ability for a person to think things through, to use his gray matter. Anyone who reads the evangelist's sermons recognizes a careful, deliberative mind behind those sermons, each point logically following one after another. (In fact, anyone who reads his sermons today mentally has to translate his King's English of 250 years ago into contemporary speech!)
"If you ask, What can reason do in religion? I answer, It can do exceeding much, both with regard to the foundation of it, and the superstructure.
"The foundation of true religion stands upon the oracles of God. It is built upon the Prophets and Apostles, Jesus Christ himself being the chief corner-stone. Now, of what excellent use is reason, if we would either understand ourselves, or explain to others, those living oracles! And how is it possible without it to understand the essential truths contained therein? a beautiful summary of which we have in that which is called the Apostles' Creed. Is it not reason (assisted by the Holy Ghost) which enables us to understand what the Holy Scriptures declare concerning the being and attributes of God?---concerning his eternity and immensity; his power, wisdom, and holiness? It is by reason that God enables us in some measure to comprehend his method of dealing with the children of men; the nature of his various dispensations, of the old and new covenant, of the law and the gospel. It is by this we understand (his Spirit opening and enlightening the eyes of our understanding) what that repentance is, not to be repented of; what is that faith whereby we are saved; what is the nature and the condition of justification; what are the immediate and what the subsequent fruits of it. By reason we learn what is that new birth, without which we cannot enter into the kingdom of heaven; and what that holiness is without which no man shall see the Lord. By the due use of reason we come to know what are the tempers implied in inward holiness; and what it is to be outwardly holy---holy in all manner of conversation: In other words, what is the mind that was in Christ; and what it is to walk as Christ walked."
I'll risk oversimplification and sum up Wesley's words in this way: In Christianity, you'll have to use you mind. God isn't going to fill your life with unending visions, dreams, voices, angelic visitations, miracles, signs and wonders. Sometimes you're just going to have to act on what you believe is right, a conclusion you've reached after difficult reasoning. Granted, Wesley believed that reason was supplemented by the Holy Spirit's revelation but the Spirit doesn't override our thinking processes.
Reasoning isn't always easy; conclusions aren't always apparent immediately. We'll all be baffled at times as to what to think or what to do. That doesn't, however, excuse us from thinking.
We must all use our mind; there are reasons God gave it to us!