Within every man lies a human heart: that unknown to mankind is the subconscious and it helps make up one half of your mind, the subconscious is deceitful and desperately wicked (Jeremiah 17:9). It is your responsibility each day to solicit God’s aid in circumcising that heart and daily submit to God so He will create in you a new, clean heart (Psalm 51:10).
“Thou shalt love the Lord thy God with ALL thy heart,” Christ says (Matthew 22:37). This is His command. You shall hold nothing back.
What is the state of your heart? Where is it divided? Where are there shadows? What are your areas of weakness?
A Godly man is the genuine article. He lives with singleness of heart allowing his subconscious = (the heart) and the conscious = (the spirit in man) to commune with each other in unity as one, striving diligently to think with integrity and to live in harmony with how he speaks. Singleness of heart and purity of the spirit in man means mastery of your mind. It is a heart chosen to be uncluttered with the things of the world, uncomplicated by the lusts of the flesh. To achieve such a state takes real diligence and effort, and can only be truly achieved by yielding to God.
King David kept that first and great commandment perhaps better than any human except Jesus Christ. His psalms enable us to scrutinize the most intimate details of his relationship with God and to emulate them.
“O God, thou art my God, I yearn for thee, body and soul, I thirst, I long for thee, like a land without water, weary, dry. … Thy love is more than life to me …” (Psalm 63:1, 3;). How did David achieve such an unnatural craving, such heartfelt, and Christ-like sincerity in the spirit in man that is his innermost being?
Such love is shed abroad in a human heart by the Holy Spirit, which is a gift from God (Romans 5:5). Once receiving that Spirit upon repentance and baptism, we maintain its flow and influence in our lives by (acquiring action through choice) submitting ourselves wholly to God, moment by moment. This requires training your heart. With diligence, vigor, and strength.
David trained his heart like a great general trains a soldier, demanding constant exercise to run it in its proper course. That is the only way to train something so unruly as a human heart.