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.

636. And they shall prophesy a thousand two hundred and sixty days, signifies that they shall teach, and what shall be taught, even to the end of the old church and the beginning of the new. This is evident from the signification of "to prophesy," as being to teach (See above, n. 624); here both to teach and to be taught, for this is said of "the two witnesses," which signify the good of love and charity and the truth of doctrine and faith, for these with man are what teach and what also are taught; for those who are in the goods of love and in the truths of doctrine teach, and the goods of love and the truths of doctrine are what are taught by them. It is evident also from the signification of "a thousand two hundred and sixty days," as being even to the end of the old church and the beginning of the new, for "a thousand two hundred and sixty days" have a similar signification as "three and a half," since a thousand two hundred and sixty days make three years and a half, computing three hundred and sixty days to the year, and "three and a half" signifies the end of a former state and the beginning of a new one, here the end of the former church and the beginning of the new one, for this refers here to the last time of the church. Because this is the signification of this number, it is said in the ninth verse of this chapter:

They shall see their bodies three days and a half, and shall not suffer them to be placed in sepulchers;

and afterwards in the eleventh verse:

And after three days and a half the spirit of life from God entered into them.

In these passages "three days and a half" signify the end of the old church, when no good of love or truth of doctrine whatever will be received; and also the beginning of a new church when they will be received. The end of the former church is signified by "the beast that cometh up out of the abyss shall kill these witnesses," and the beginning of the new church is signified by "the spirit of life from God entered into them." The number "a thousand two hundred and sixty" has a similar signification as "three and a half," because in the Word "ages," "years," "months," "weeks," "days," and "hours," have a like signification, for these mean merely times, and times in general and in particular, or times greater or less, equally signify states, for a greater or less time designated by numbers does not change the signification of the thing (as shown above, n.571, 633). The same number of days has a like signification in the next chapter of Revelation:

And the woman fled into the wilderness, where she hath a place prepared by God, that there they may nourish her a thousand two hundred and sixty days (Revelation 12:6).

The "woman" here means the church; the "wilderness," where she should be nourished, signifies where there is no reception of good and truth; and "after the passing of those days" signifies a new state of the church.