Heart
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.
Zechariah 14:5-7
5
You shall flee by the valley of my mountains; for the valley of the mountains shall reach to Azel; yes, you shall flee, just like you fled from before the earthquake in the days of Uzziah king of Judah. Yahweh my God will come, and all the holy ones with you.
6
It will happen in that day, that there will not be light, cold, or frost.
7
It will be a unique day which is known to Yahweh; not day, and not night; but it will come to pass, that at evening time there will be light.
