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 Containers out of all items in the game, and is the only one that grants three Red Heart Containers.
Between this item, The Mind, and The Soul, The Body is the only one that cannot be summoned via the Lemegeton.
The Mind and 
The Soul, are references to the Three Primes of Alchemy.
Lemegeton.
The Lost Unlocks 
??? (Boss) Unlocks 
The Binding of Isaac: Rebirth
