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.

196. In ancient times people who relied on sensory evidence rather than matters of revelation were called serpents. Nowadays the position is even worse, for not only are there people who believe nothing unless they can see it with their eyes and apprehend it with their senses, there are also those who confirm themselves in that attitude by means of facts unknown to the most ancient people, and who in so doing blind themselves very much more. To make known how people who draw conclusions about heavenly things on the basis of sensory evidence, facts, and philosophical arguments, so blind themselves that they subsequently see and hear absolutely nothing, and who are not only the deaf serpents but also the far more deadly flying serpents, mentioned in the Word as well, let their belief concerning the spirit serve as an example.

[2] Anybody who is sensory-minded, that is, whose belief is rooted solely in the senses, denies the existence of the spirit because he does not see it. He says, 'Because I do not feel it, it is nothing; what I see and touch, I know to exist'. Anybody who is factually-minded, that is, who bases his conclusions on factual knowledge, says, 'What is the spirit but perhaps breath, or vital heat, or something else known to me, which is dissipated when it comes to an end? Do not animals as well have a body, and senses, and something analogous to reason? Yet people say that animals are destined to die but man's spirit to live.' In this way they deny the existence of the spirit. Philosophers, men wishing to be more incisive than everybody else, speak of the spirit in terms which they themselves are not clear about since they argue about them. They contend that not a single expression is applicable which in any way derives from what is material, organic, or spatial. In this way they dismiss the spirit from their ideas, and as a result it passes from their notice and becomes nothing at all.

[3] Those among them however who are more sensible say that the spirit is thought, but when they begin to reason about thought they at length conclude, since they separate thought from substance, that it will disappear when the body breathes its last. In this way everyone who reasons on the basis of sensory evidence, facts, and philosophical arguments denies the existence of the spirit, and in denying its existence never believes anything that is said about the spirit or about spiritual things. But if indeed the simple in heart are questioned they say that they know that the spirit exists because the Lord has said that they will live after death. Instead of smothering their rationality they nurture it by means of the Word of the Lord.