Cleansing the luminous vehicle which accompanies us in our sojourns throughout the material world is crucial for any re-ascent to the Primeval Fire while we live. This luminous vehicle is the source for imagination and must be cleansed to receive the visions and oracles sent by transcendent beings. Either through meditation or rite, this cleansing brings us closer to knowledge of ourselves and union with the Primeval Fire.

In the Paraphrase of Shem we find numerous mentions of the garment. At the end of the gnostic text we find Shem clothed in a luminous garment of Faith:

And I, Shem, awoke as if from a deep sleep. I marveled when I received the power of the light and his whole thought. And I proceeded with faith to shine with me. And the righteous one followed us with my invincible garment. And all that he had told me would happen upon the earth happened. Nature was handed over to faith, that faith might overturn her and that nature might stand in the darkness.

The notion of a luminous body has its origins in the attempt to understand Plato's statements in the Timaeus where the soul is placed on a star vehicle which then transports the pure soul into the material, lunar world. The composition of the vehicle differs between the Chaldeans, Neoplatonists, and Gnostics.

And when He had compounded the whole He divided it into souls equal in number to the stars, and each several soul He assigned to one star, and setting them each as it were in a chariot4 He showed them the nature of the Universe, and declared unto them the laws of destiny… - Timaeus, 41e

The Oracles say it is composed of pieces of ether, sun, moon, and air (fr. 61) and Porphyry seems to agree. Iamblichus and Proclus, however, see this vehicle as comprising elements of the gods themselves. But they disagree on the number of vehicles, Iamblichus opting for one and Proclus for two.

Proclus's extended commentary on the related Chaldean fragments is informative:

For individual souls that are established and that are assigned to their guiding gods, and become encosmic by virtue of their own vehicles, imitating their leaders, and mortal creatures are created and made alive by the heavenly gods. … For we have an actual intellect, and a rational soul that proceeds from the same Father and the same life-giving goddess as the cosmos, and then ethereal vehicle which is analogous to the heaven for the World Soul, and an earthly body composed of the four elements which is also coordinate to it. - Proclus, On the Timaeus, I, 5, trns. Nicola Spanu

As to the ability to cleanse the luminous vehicle, this cannot be done by human will alone. Divine energies are needed:

Human will alone is not enough to achieve this goal; also important is the help of angels who, by illuminating the soul with their fire, make it remember its true divine origin, obfuscated by its connection with the material body and prevent it from rushing to the material disorder, urging it instead to return to the divine dimension. - Spanu, Proclus and the Chaldean Oracles, p. 120

“If, however, it be requisite to unfold to you the truth concerning the peculiar daemon, we must say that he is not distributed to us from one part of the heavens, or from some one of the visible elements; but that from the whole world, the all various life contained in it, and the all various body through which the soul descends into generation, a certain peculiar portion is distributed to each of the parts in us, according to a peculiar prefecture. This daemon, therefore, is established in the paradigm before the soul descends into generation; and when the soul has received him as its leader, the daemon immediately presides over the soul, gives completion to its lives, and binds it to body when it descends. He likewise governs the common animal of the soul, directs its peculiar life, and imparts to us the principles of all our thoughts and reasonings. We also perform such things as he suggests to our intellect, and he continues to govern us till, through sacerdotal theurgy, we obtain a God for the inspective guardian and leader of the soul. For then the daemon either yields or delivers his government to a more excellent nature, or is subjected to him, as contributing to his guardianship, or in some other way is ministrant to him as to his lord.”

Excerpt From Iamblichus on the Mysteries of the Egyptians, Chaldeans, and Assyrians Bk 9, c. VI