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.

5502. 'And they trembled [turning] a man to his brother' means the dread shared by them all. This is clear from the meaning of 'trembling' as dread, and from the meaning of 'a man to his brother' as shared by all, as just above in 5498. The reason why fear is expressed by these two phrases, by 'their heart went out' and 'they trembled', is that one has reference to the will and the other to the understanding. For it is quite usual in the Word, especially in the prophetical part, for the same matter to be described twice, though with a change of words. Anyone unacquainted with the hidden reason for this may imagine that it is pointless repetition; but that is not the case. One expression has reference to good, the other to truth; and because good belongs in the will and truth in the understanding, one has reference at the same time to the will and the other to the understanding. The reason for this is that in the Word everything is holy, and this holiness comes from the heavenly marriage, which is the marriage of goodness and truth. This being so, heaven is present within the Word, and so too is the Lord, the All in all of heaven - present so fully that He is the Word. The Lord's two names Jesus Christ entail the same, the name Jesus entailing Divine Good and the name Christ Divine Truth, see 3004, 3005, 3008, 3009. From this it is also evident that the Lord is present in every part of the Word, present so fully that He is the Word itself. Regarding the marriage of goodness and truth, which is the heavenly marriage, in every detail of the Word, see 683, 793, 801, 2516, 2712, 5138. From this a further conclusion may be reached, that to live in expectation of heaven a person must have within him not only truth that is the truth of faith but also good that is the good of charity. Otherwise no heaven is present within him.