To build something generally means to put together a variety of simpler pieces to make a useful and more complex structure, as to build a house out of wood or bricks, and it is commonly used this way in the Word. In the land of Shinar men wished to build a tower, and in the new testament Jesus advised that a wise man should build his house on a rock. But in a representative sense the meaning is to build a mental and spiritual structure, like the doctrine of a church or the individual concepts of spiritual reality in a single mind. The building materials are representative also. The tower of Babel was built of brick, which is man-made rock, or representatively, man-made "truths", that is"truths" not from God but ideas of spiritual reality thought out by men. The house that the wise man would build was founded on a natural or "God-made" rock, which means a truth from the Word.

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.