Augustine of Hippo, on Matt 5:33

“Again you have heard that it was said to them of old, Thou shalt not forswear thyself: but thou shalt perform thy oaths to the Lord.”

“(Serm. in Mont. i. 17.) Or; It is added, By the Heaven, &c. because the Jews did not consider themselves bound when they swore by such things. As if He had said, When you swear by the Heaven and the Earth, think not that you do not owe your oath to the Lord your God, for you are proved to have sworn by Him whose throne the heaven is, and the earth His footstool; which is not meant as though God had such limbs set upon the heaven and the earth, after the manner of a man who is sitting; but that seat signifies God’s judgment of us. And since in the whole extent of this universe it is the heaven that has the highest beauty, God is said to sit upon the heavens as shewing divine power to be more excellent than the most surpassing show of beauty; and He is said to stand upon the earth, as putting to lowest use a lesser beauty. Spiritually by the heavens are denoted holy souls, by the earth the sinful, seeing He that is spiritual judgeth all things. (1 Cor. 2:15.) But to the sinner it is said, Earth thou art, and unto earth thou shalt return. (Gen. 3:19.) And he who would abide under a law, is put under a law, and therefore He adds, it is the footstool of His feet. Neither by Jerusalem, for it is the city of the Great King; this is better said than ‘it is mine;’ though it is understood to mean the same. And because He is also truly Lord, whoso swears by Jerusalem, owes his oath to the Lord. Neither by thy head. What could any think more entirely his own property than his own head? But how is it ours when we have not power to make one hair black or white? Whoso then swears by his own head also owes his vows to the Lord; and by this the rest may be understood.”

Imported from an open dataset — not yet checked against the printed edition.