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“Hear, O Israel! The LORD our God, the LORD is one! You shall love the LORD your God with all your heart, with all your soul, and with all your strength. And these words which I command you today shall be in your heart. You shall teach them diligently to your children, and shall talk of them when you sit in your house, when you walk by the way, when you lie down, and when you rise up. You shall bind them as a sign on your hand, and they shall be as frontlets between your eyes. You shall write them on the doorposts of your house and on your gates” (Deuteronomy 6:4-9).
There are two qualities which characterize mankind’s relationship with God: the head and the heart; that is, the thinking and the feeling.

All human relationships are a combination of thinking and feeling. Take one of the most basic relationships between a man and his food. If I go to a buffet, I will most likely load my plate up with food that I recognize. Occasionally, I will try a new food (and there are very few of these foods I won’t try again). In order to like a particular food (feeling), I must first know if I like it or not (thinking). I know I like certain foods because of my knowledge of them: “Pizza tastes good. I know this because I have experience with what pizza is like.” Another type of food, however, that I have no knowledge of, I cannot say with certainty that I like it because I have no knowledge of it. I can assume I will like it or assume I will dislike it, but I need to have an experience with it in order to know for sure.

Or take a more complicated relationship between a man and a woman. It would be foolish for a man to say, “I like that girl” without ever having spoken with her or ever having spent time with her. He may be speaking strictly with his feeling (“she’s pretty”), but in order to know her, he must engage his mind.

On the other hand, if a man knows everything there is to know about a particular woman - her favorite color, her life story, her interests, her dislikes, her love language, her desires - yet only robotically acts according to his knowledge, the relationship will be doomed to failure.  His knowledge must compel him to a passionate pursuit of her.

In our relationship with God, the head and the heart are equally impactful. Who can worship what they do not know? And who can worship properly what they do not authentically and genuinely desire to worship? The head and the heart should never be separated. Theology (study of God) and doctrine (systems of truth) are meaningless if they lead us only to engage in academic exercises about God. They are only fruitful if they lead us to humble worship in our hearts. Seeking emotional, spiritual experiences apart from proper knowledge and fear of God is equally meaningless, since they lead us not to the worship of the true God, but of our own feelings at the given moment.

C.S. Lewis says in his book The World’s Last Night, “[Martin] Luther surely spoke very good sense when he compared humanity to a drunkard who, after falling off his horse on the right, falls off it next time on the left.” The over zealousness of knowledge will lead to great arrogance and pride. Beware of this, lest we forget about the mercy and kindness of God, which is what leads us to repentance. Likewise, the over zealousness of emotional promptings and leadings will lead to misguided worshippers. Beware of this as well, lest we forget about the order and justice of God, which is what gives reason to our worship. The Christian must take special care to guard between the two extremes, and instead engage in study of God with thanksgiving and praise.

I have been at both extremes. I have worshipped God in immaturity, merely praising Him out of emotion, with little knowledge of who He actually is and what He requires of me. I have also spent much time in the study of God without engaging the heart, which led to an argumentative disposition, demanding that others agree with my interpretative view, but becoming more and more a resounding gong and a clanging cymbal for I had not love.

In Deuteronomy, God addresses both the mind and the spirit. He tells them who He is: “I am the LORD your God, and I am one. There is none other like Me.” This engaged the mind, so that they could know who saved them from Egypt and who they are to respond to in worship. He then tells the Israelites how to worship Him: “Love Me with all your heart, soul, and strength.” And then God exhorts them to teach the next generation and to speak about His great works in order to pass on the passion to His future people.

As outlined in Deuteronomy, the responsibility of humans is to teach others about God; yet, it is the Lord who will write His Word on their hearts. Changing that teaching into heartfelt, spiritual worship and joy is the work of God. (Or, in many cases, it is the teaching of the Word that will lead to rejection of God and instead bring about condemnation.)

Therefore, it is good to engage our minds in the spiritual disciplines of meditation, study, prayer and fasting, evangelism and teaching, singing, journaling, memorization, and accountability. But if these disciplines do not lead to spiritual transformation, there is much about which to be concerned. Be aware of the “knowledge that puffs up” by seeking God in repentance to give you the “love that builds up" (1 Corinthians 8:1-3).

In summary, R.C. Sproul writes in the introduction of his book Essential Truths of the Christian Faith, the following regarding the importance of head and heart:
“The influence of existential philosophy has been massive. We have become a sensuous nation. Even our language reveals it. May seminary students repeatedly write like this on their exam pages: ‘I feel it is wrong that…’ or ‘I feel it is true that….’ I invariably cross out their word feel and substitute the word think. There is a difference between feeling and thinking. 
There is a primacy of the mind in the Christian faith. There is also a primacy of the heart in the Christian faith. Surely that paradoxical declaration sounds like a contradiction. How can there be two primacies? Something must be ultimately prime. Of course we cannot have two different primacies at the same time and in the same relationship. When I speak of two different primacies, I mean with respect to two different matters.
With respect to the primacy of importance, the heart is first. If I have correct doctrine in my head but no love for Christ in my heart, I have missed the kingdom of God. It is infinitely more important that my heart be right before God than that my theology be impeccably correct. 
However, for my heart to be right, there is a primacy of the intellect in terms of order. Nothing can be in my heart that is not first in my head. How can I love a God or a Jesus about whom I understand nothing? Indeed, the more I come to understand the character of God, the greater is my capacity to love Him.”

Lord, temper me, I pray. Temper and balance my quest for knowledge of You with mercy, kindness, and love with others. Conform me to Your image, oh God. Amen.