The heart means love. A good heart means love to the Lord and to the neighbor, while a hard or stony heart means the love of self or the world -- riches and things. When the psalmist asks the Lord to search his heart, he wants the Lord to see what it is that he loves. And we are what we love. What we eat may form our earthly body, but it's only temporary, what we love forms our spiritual body, beautiful or ugly as we have chosen. It's interesting to note that the first multi-cellular motion of our embryo is the pulsating that starts in a twist of blood vessel that is to become our heart, and the last motion of our natural body is our heartbeat. It is there for all of our natural life. And of course there is a beating heart in our spiritual bodies when we come to put them on.

'A shield' signifies defense which is trusted against evils and falsities. In respect to the Lord, it signifies defense, and in respect to people, confidence in the Lord's protection. This is because it was a protection for the breast, and 'the breast' signifies good and truth, good because of the heart in it, and truth because of the lungs. In an opposite sense, 'shield' denotes evils and falsities which are used to wage combat, and is used as a defense in Jeremiah 46:3-4 among other passages.

(Odkazy: Arcana Coelestia 1788)