The Barddas of Iolo Morganwg, Vol. I., ed. by J. Williams Ab Ithel, , at sacred-texts.com
Disciple and his Master.
Disciple. Why is Iau (yoke) given as a name for God?
Master. Because the yoke is the measuring rod 6 of country and nation in virtue of the authority of law, and is in the possession of every head of family under the mark of the lord of the territory, and whoever violates it is liable to a penalty. Now, God is the measuring rod of all truth, all justice, and all goodness, therefore He is a yoke on all, and all are under it, and woe to him who shall violate it.
221:5 p. 220 "A yoke." It would appear, rather, that the iau, or yoke, being the badge of power on the part of him who imposed it, was so designated from , p. 221 a combination of Bardic symbols, which indicates preservation, creation, and destruction, and which was one of the earliest forms of the Divine Name. Iolo Morganwg interprets "Iau" as meaning "the recent, or last manifestation of the Deity--Mithras, Mithra;" from the adjective, which literally signifies younger.
221:6 The yoke, as a measuring rod, is mentioned in the Welsh Laws; it follows, therefore, that this catechetical fragment must have been composed when those laws were in force.