To Florus 3.40

To illustrate and confirm the fairness of his judgment, God uses an oath, adding a solemn pledge to the authority of his decree. The apostle understood this manner of speaking when he explained to the Hebrews: ‘God, wishing to show the heirs of the promise the unchangeable nature of his purpose, intervened with an oath, so that through two unchangeable things, in which it is impossible for God to lie, we might have the strongest encouragement’ (Hebrews 6:17–18).