The designs of these items appear to be that of Triquetra, a Christian symbol of the Trinity.
The item's description, along with those of The Mind and The Soul, are references to the three attributes commonly ascribed to God in Christian theology: omniscience, omnipotence, and omnipresence. For The Body, it is omnipresence, the ability to be everywhere, thus to "feel all".
By itself (without other items/pickups), the Body grants the most amount of red heart container out of all items in the game, and is the only one that grants three Red Heart Containers.