The cherubim of the Hebrew Bible do two things, and almost everything said of them falls under one heading or the other. They guard a threshold, and they carry or flank a throne.
The guarding comes first. At the close of the third chapter of Genesis, after the expulsion, cherubim are stationed east of the garden with a flaming sword turning every way, to keep the way to the tree of life. The verb is one of watch and of prevention, and the scene is a closed door with something formidable standing in front of it.
The throne function is the larger one. Exodus gives two cherubim of beaten gold at the two ends of the mercy seat, wings spread upward and faces turned toward each other, and names the space between them as the place where God will speak. Solomon's inner sanctuary holds a far larger pair, and a phrase describing God as enthroned upon the cherubim recurs through the historical books and the Psalms. Ezekiel's tenth chapter brings the two functions together, identifying the cherubim there with the living creatures who bear the chariot of the opening vision.
Both functions have close parallels in the art of the surrounding cultures, where winged composite beasts flank gateways and support seats in exactly these two situations. The rank the Kabbalistic lists call kerubim inherits all of it, and inherits none of the later decorative infant, which belongs to a quite separate history.