So it really is a way for a Mage to shed his body of flesh and blood entirely.
Once an apprentice advanced and became a Mage, the soul was no longer a frail bundle of information that had to shelter inside a fleshly body. After the transformation brought about by ether bestowal, the soul gained the capacity to bear mana, and mana would go on strengthening that soul—yet the body still could not contain mana.
For an ordinary elemental Mage, a body of blood and flesh became the very burden that blocked him from obtaining energy, and so by this stage a Mage had to set about using his soul to command the elements and get himself a new body.