In these verses Jesus compares our garments against the innate Beauty of lilies. Nothing is more earthly beautiful than nature, and we need light to see nature's beauty. Nothing reflects beauty in darkness.
In ancient times, King's robes were elaborate, ornate, made of silk and valuable textiles, embroidered with gold and silver. King's robes were beautiful works of art. The wisest king who has ever lived, King Solomon, was not clothed as perfectly as the lilies of the field. Why? Because God clothes the lilies.
God desires to clothe us, too, but not with silk and linen, or with gold, silver, pearls and precious jewels, but with the very presence of the Glory of Jesus: "Arise, shine; for thy light is come, and the glory of the Lord is risen upon thee."
~dkg