Do you have any associations to holding something against your chest? Have you ever held a baby or a pet there?

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Also, a T'ai Chi practitioner I know talked about the sensation that your are holding a ball of energy between your hands in front of your chest. You might not be a T'ai Chi practitioner, but some of these associations might be to archetypal factors (things that arise spontaneously in all humans)

Like holding something precious against your chest seems to be universal. (Maybe another one is holding a stuff animal.)

I mention these things just to see if they click for you.

About the grain of sand, aren't there some parables about each grain of sand being precious to God, or something about how there are as many people as grains of sand but God cares about all of them? It's an interesting feeling, putting such a quality of rapt attention, and taking so much peace, from a tiny thing (which is only one of billions).