From the verse on the left (Mark 12:30) we discover that a pure heart requires every bit of affection that we have - with all our heart. If this is not clear, Jesus mentions all our soul, all our mind and all our strength. Purity means 'rid of impurities.' Or in this case, we have one chief love and nothing divides or distracts our attention from it.
God has designed us to serve Him from a pure heart. We are not saying this is easy. In fact, we have explained that it is impossible without God. At the same time, though, we should not make any excuses for our lack of affection for Him. His love and faithfulness has not lessened a bit. The problem is with us. We understand that the Lord is looking for that person who has a pure heart.
But the goal of our instruction is love from a pure heart and a good conscience and a sincere faith. (1 Timothy 1:5).
Upon our salvation, we gain a new heart born from the Spirit. The Spirit keeps this new source of affection alive. From this new heart spring forth all sorts of desires to serve and love God. This in turn helps us to care for others.
The Old Testament gives us is very clear picture of this process by the phrase 'circumcision of the heart.' We can understand that the hardness originally covering our hearts actually separated us from everything that was good and spiritual. We were a world to ourselves. We could not see beyond this world nor did we desire to do so. The Holy Spirit, though, in regenerating our hearts actually cuts this fold of skin away and exposes our hearts before Him, making us very vulnerable.
"Circumcise then your heart, and stiffen your neck no more. (Deuteronomy 10:16).
"Moreover the LORD your God will circumcise your heart and the heart of your descendants, to love the LORD your God with all your heart and with all your soul, in order that you may live. (Deuteronomy 30:6).
The new heart then frees us to respond to the things of the Spirit. We are brought into contact with the things of God and therefore can respond to them. In the new birth a whole new creature comes awake with the intrusion of the Spirit upon our lives.
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We will come back to this hardening for it is here the Christian struggles in his Christian growth. However, let me conclude this section with a more thorough description of what happens by the most famous American theologian, Jonathan Edwards. If you can stay with words (older English), you will greatly benefit from his description of what happens when a person becomes a Christian from the perspective of the heart.
Let us go on now and get yet more practical. For which of us feel confident that his worship of God utilizes his total person? We have a new heart, and yet we find ourselves committing sin. Why do we have a divided heart? Are we still unbelievers or are we weak Christians? How can we get a pure heart to worship our great God? Continue on!