Exod 28:8

“Which ephod is also rightly ordered to be made of gold, blue, purple, twice dyed scarlet, and fine twined linen, that it may be shewn by how great diversity of virtues the priest ought to be distinguished. Thus in the priest's robe before all things gold glitters, to shew that he should shine forth principally in the understanding of wisdom. And with it blue, which is resplendent with aerial colour, is conjoined, to shew that through all that he penetrates with his understanding he should rise above earthly favours to the love of celestial things; lest, while caught unawares by his own praises, he be emptied of his very understanding of the truth. With gold and blue, purple also is mingled: which means, that the priest's heart, while hoping for the high things which he preaches, should repress in itself even the suggestions of vice, and as it were in virtue of a royal power, rebut them, in that he has regard ever to the nobility of inward regeneration, and by his manners guards his right to the robe of the heavenly kingdom. ... But with gold, blue, and purple, twice died scarlet is conjoined, to show that all excellences of virtue should be adorned with charity in the eyes of the judge within; and that whatever glitters before men may be lighted up in sight of the hidden arbiter with the flame of inward love. And, further, this charity, since it consists in love at once of God and of our neighbour, has, as it were, the lustre of a double dye. He then who so pants after the beauty of his Maker as to neglect the care of his neighbours, or so attends to the care of his neighbours as to grow languid in divine love, whichever of these two things it may be that he neglects, knows not what it is to have twice dyed scarlet in the adornment of his ephod. But, while the mind is intent on the precepts of charity, it undoubtedly remains that the flesh be macerated through abstinence. Hence with twice dyed scarlet fine twined linen is conjoined. For fine linen springs from the earth with glittering show: and what is designated by fine linen but bodily chastity shining white in the comeliness of purity? And it is also twisted for being interwoven into the beauty of the ephod, since the habit of chastity then attains to the perfect whiteness of purity when the flesh is worn by abstinence. And, since the merit of affliction of the flesh profits among the other virtues, fine twined linen shews white, as it were, in the diverse beauty of the ephod.”