What does the gospel mean by "loving God with all Your heart"? To understand this, we should first recognize that the heart is the fountain from which springs all human emotions and desires.
The area of the human brain that responds to these emotions and desires merely reflects the activities of the heart. The brain does not initiate emotions and desires.
In Mark 7:21-22, Jesus said, "For from within, out of man's heart come evil thoughts, sexual immorality, theft, murder, adultery, greed, malice, deceit, lewdness, envy, slander, arrogance, and folly."
But as the heart is capable of evil deeds, so it is capable of love, compassion, understanding, tolerance, kindness, forgiveness and forbearance.
It could be said the heart is like a knife. In one hand, it can cut generous slices of bread to feed the poor and needy; yet in another hand, it can become an instrument of death. It all depends in whose hand lies the knife.
Similarly, whether the content of the heart is acted upon depends on who controls it. All the emotions and desires of the heart must first be approved by the conscious mind, and this then issues operational instructions to the body to put them into effect.
Without the approval and issuance of operational instructions by the conscious mind, the body cannot put the emotions and desires of the heart into effect, since the body cannot act on its own volition, except in those rare cases where it acts involuntarily, as in a muscle twitch.
But, who informs the conscious mind? The subconscious mind does, which in turn, is informed by the spirit residing in the soul. Thus, the spirit that resides in the soul ultimately controls the heart and the emotions and desires that are given physical expression by the body.
At all times, the soul is occupied either by the Spirit of God or the demons of Satan, except during the brief period following the departure of the Holy Spirit from a corrupted soul (Luke 11:24-26).
Like vagabonds, the demons of Satan ceaselessly prowl the earth in search of corrupted souls to occupy. When they find such souls, they are drawn to them like vultures are drawn to rotten carcasses. Once in possession of the corrupted soul, the demons' first order of business is to control the mind of the soul, by infiltrating the subconscious mind.
Since the subconscious mind informs the conscious mind, Satan and his demonic agents are then able to ensure that the conscious mind would approve all the negative emotions and desires of the heart, and accordingly issue operational instructions to the body to put them into effect.
In this way, the will of Satan is done; while all along, the possessed person in whom resides the corrupted soul, continues to believe he is in full control of himself, and every word from his mouth, and every deed of his hands are his own.