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.

Stones in the Bible in general represent truths, or things we know concerning the Lord and what He wants from us and for us in life. This is why the people of Israel built altars of stone, and is also why stoning was a principal form of capital punishment (using truth to destroy falsity, or in the negative sense using falsity to destroy truth). It is also why precious stones are described in such detail on Aaron's breastplate and ephod, and also in the New Jerusalem in Revelation; precious stones represent true ideas directly from the Lord with the various colors showing various forms of love. Stones are not alone in representing truth, of course -- it sometimes seems that almost everything in the Bible represents either true ideas or desires for good. But that makes sense, since our thoughts and our desires together are everything we are in life, and the interplay between them is what life is all about. The many ways they are represented in the Bible reflect the incredible variety in our feelings and thoughts, though we can only distantly understand how those representations work. In the case of stones, in their weight, strength and permanence they tend to represent true ideas that come from a desire for good, the understanding we can have if we are truly good and loving -- and in the highest sense the exalted ideas that come from the Lord's love. Those ideas are ones that are not easily moved or changed, and make wonderful foundations for the things we want to build in our spiritual lives.