What means: "Above all else, guard your heart, for everyting you do flows from it" in Proverbs 4:23?

The Bible explains to us that it is from the heart, in a metaphorical sense, that man's intentions come:
"Above all else, guard your heart, for everyting you do flows from it", Proverbs 4:23.
"For where your treasure is, there your heart will be also", Matthew 6:21.
"Again Jesus called the crowd to him and said, "Listen to me, everyone, and understand this. Nothing ourside a person can defile them by going into them. Rather, it is what comes out of a person that defiles them."
After he had left the crowd and entered the house, his disciples asked him about this parable. "Are you so dull?" he asked. "Don't you see that nothing that enters a person from the outside can defile them? For it doesn't go into their heart but into their stomach, and then out of the body."
He went on: "What comes out of a person is what defiles them. For it is from with in, out of a person's heart, that evil thoughts come - sexual immorality, theft, murder, adultery, greed, malice, deceit, lewdness, envy, slander, arrogance and folly. All these evils come from inside and defile a person." Mark 7:14-23

According to biblical thought the heart is the place where our treasure of goodness or perversion lies and that treasure bears fruit, and these fruits can be fruits of life or death: "The acts of the flesh are obvious: sexual immorality, impurity and debauchery; idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissension, factions and envy, drunkenness, orgies and the like. I warn you, as I did before, that those who live like this will not inherit the kingdom of God.
But the fruit of the spirit is love, joy, peace, forbearance, kindness, goodness, faithfulness, gentleness and self-control. Against such things there is no law"; Galatians 5:19-23.
Let's remember that there is a parable of Jesus referring to the treasure of the heart, the parable of the hidden treasure: "The kingdom of heaven is like treasure hidden in a field. When a man found it, he hid it again, and then in his joy went and sold all he had and bought that field." Matthew 13:44. The kingdom of God according to this parable is the change of heart, a change towards God and the neighbor.
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