Interpretation of the Bible
You shall not wear combined fibers, wool and linen together.
Clothes make the (wo)man. Or in the case of living biblically, clothes that are made from pure fabrics are a must when selecting wardrobe.
Many religious followers live by the bible through their clothing. Not mixing wool and linen is specifically mentioned in the bible without much explanation.
Yet that doesn't stop a flow of ideas as to the meaning of this prohibition. One theory stems from the story of Cain and Abel. Abel brought an offering of sheep (wool) to God and Abel offered God flax (source of linen). Mixing fibers didn't work out for the feuding brothers, and literal believers figure it probably won't work for them either.