The number three in the Bible represents completeness. That's why Jesus rose on the third day after the Crucifixion -- his transformation was complete. It's why Elijah stretched himself on the dead child three times, why Jonah was in the belly of the fish for three days, why the Lord called Samuel three times, and many more. It's also reflected in the fact that there are three levels of heaven, three levels of hell, three levels to human life and, ultimately, three aspects of the Lord Himself: Father, Son and Holy Spirit.

9866. 'One row' means a group of three there existing as one. This is clear from the meaning of 'row' as a group of three; for three stones constituted it, and 'three' means that which is complete from beginning to end, 2788, 4495, 7715, 9198, 9488. They are said to exist as one because a sequence of three makes one; for the resulting presence of three together, side by side at the lowest level, corresponds to the consecutive order which has given rise to their presence together on that level and maintains it, see 9825. So it is that the three heavens make one on the last and lowest level; and the same applies in each heaven. The origin of this lies in God Himself, in whom there is a Trinity, consisting of His Essential Divinity, Divine Humanity, and Divine Proceeding, which make one. And this Divine Trinity making One is the Lord. From all this it may be seen why in each row there were three stones and that a group of three existing as one is meant by each row. The reason why there were four rows is that in heaven there are two kingdoms, the celestial kingdom and the spiritual kingdom, and in each there is an internal part and an external. The internal and external of the celestial kingdom was represented by the two rows on the right side of the breastplate, and the internal and external of the spiritual kingdom by the two rows on its left side. For the breastplate was a square when doubled over.