Calvin's Commentaries, Vol. 4: Harmony of the Law, Part II, tr. by John King, [1847-50], at sacred-texts.com
We now come to the third part of the external service of God, which will bring us to the end of our exposition of the Second Commandment. We have, then, now to treat of the sacred oblations, the first place amongst which I have thought it best to give to the loaves, which had their peculiar table opposite the candlestick on the north side, as we saw in the construction of the Tabernacle; for although the mention of them will recur elsewhere, yet, since they were offered separately, and placed before the Ark of the Covenant, as it were in God’s sight, they must not be treated of apart from the sacrifices. I have already explained that this was no ordinary symbol of God’s favor, when He descended familiarly to them, as if He were their messmate. They were called “the bread of faces,” 227 because they were placed before the eyes of God; and thus He made known His special favor, as if coming to banquet with them. Nor can it be doubted but that He commanded them to be twelve in number, with reference to the twelve tribes, as if He would admit to His table the food offered by each of them. The “two tenths” make the fifth part of the epah. And it is plaia indeed that this rite was thus accurately prescribed by God, lest diversity in so serious a matter might gradually give birth to many corruptions. In the word “tenths,” He seems to allude to the tax which He had imposed on the people, that thus the holiness of the loaves might be enhanced. But why He required two “tenths” rather than one I know not, nor do I think it any use more curiously to inquire. I refer to the frankincense the words, “that it may be on the bread for a memorial:” as if it were said that the bread, seasoned by the smell of the incense, would renew the memory of the children of Israel, so that they should be of sweet savor before God. Others translate it “a monument” instead of “for a memorial,” but with the same meaning. But although some think that the bread itself is called a memorial, it is more applicable to the frankincense; for it is afterwards added, that the incense should be at the same time a burnt sacrifice, viz., because in it the bread was, as it were, offered in burnt sacrifice.
לחם-פנים “panes facierum.” In Ex 25:30, as in several other places, the shew-bread of A. V. is a translation of these words. — W