We often talk about the heart when discussing spiritual matters but this can seem frustratingly vague to those who don't grasp what is meant by that. It is not instinct, it is not emotion and it is certainly not the regular mind, It is something more than any of these. I came across a definition the other day which makes a lot of sense. The heart is where the blood meets the spirit. I like this because it implies the union of spirit and matter to make something more than either of them on its own which, to my way of thinking, is the whole point of creation, evolution, the whole game of life. Through creation God expresses himself and through expressing himself he knows himself better. He also knows love which he cannot really do in his unmanifested solitary state. Strange but true.
The heart is the spiritual organ of perception roughly equivalent to the intuition. It is feeling but not feeling as we generally know it because it is both subjective and objective at the same time. This is how God sees things and it is the simplest way of seeing in which knowing and being are all one. What the heart feels, it knows and what it knows it is. Obviously at our early stage of development this is intermittent and incomplete but the fact remains that the awakening of the heart is the entry requirement for spiritual life. For many people just becoming aware of the heart in its spiritual sense there is much confusion between it and their own emotions with the latter muddying the purity of the spiritual water. But if one clears one's mind of its ideological conditioning and wishful thinking, and moves beyond feelings based on personal likes and dislikes to what you might think of as the Feeling Principle which for Christians would be feeling rooted in the reality of Christ rather than centred on their own little self, then there is a gradual cleansing of emotion so that it can be transformed into the feeling/knowing of the heart. Jesus said "as a man thinketh in his heart so is he". Note that he said thinks not feels. The heart thinks as it feels and it feels as it thinks. On this level there is no difference.
Blood means something spiritually. It is what you are. It is not just the red stuff that is pumped round your veins by the heart muscle. It contains something intrinsic to your self which previous generations understood. (As in, we are of the same blood.) Where the blood, which is the essence of you, meets spirit which is the essence of God, there is the spiritual heart and that is where the soul blossoms. When this meeting takes place you then rise up out of your normal material self into spiritual being and see the world anew. Those who have not undergone this renewal might dismiss it and its fruits, which are spiritual insight and knowledge, as imaginary but if they purified their blood, which means cleansed the soul of its materialistic impulses, they would understand. Then they too would awaken to the reality of the heart and its pristine knowledge of God.