Athanasius of Alexandria

Now the so-called gods of the Greeks, unworthy of the name, are faithful neither in their essence nor in their promises. They do not abide everywhere. The local deities come to nought in the course of time and undergo a natural dissolution.… But the God of all, being one really and indeed and true, is faithful, who is ever the same.… He is ever the same and unchanging, deceiving neither in his essence nor in his promise. As again says the apostle writing to the Thessalonians, "Faithful is he who calls you, who also will do it"; for in doing what he promises, he is faithful to his words. And he thus writes to the Hebrews as to the word's meaning "unchangeable": "If we believe not, yet he abides faithful; he cannot deny himself."