1 The rule of truth which we hold, is, that there is one God Almighty, who made all things by His Word, and fashioned and formed, out of that which had no existence, all things which exist. Thus says the Scripture, to that effect “By the Word of the Lord were the heavens established, and all the might of them, by the spirit of His mouth.” And again, “All things were made by Him, and without Him was nothing made.” There is no exception or deduction stated; but the Father made all things by Him, whether visible or invisible, objects of sense or of intelligence, temporal, on account of a certain character given them, or eternal; and these eternal things He did not make by angels, or by any powers separated from His Ennœa. For God needs none of all these things, but is He who, by His Word and Spirit, makes, and disposes, and governs all things, and commands all things into existence—He who formed the world (for the world is of all)—He who fashioned man—He [who] is the God of Abraham, and the God of Isaac, and the God of Jacob, above whom there is no other God, nor initial principle, nor power, nor pleroma,— He is the Father of our Lord Jesus Christ, as we shall prove. Holding, therefore, this rule, we shall easily show, notwithstanding the great variety and multitude of their opinions, that these men have deviated from the truth; for almost all the different sects of heretics admit that there is one God; but then, by their pernicious doctrines, they change [this truth into error], even as the Gentiles do through idolatry—thus proving themselves ungrateful to Him that created them. Moreover, they despise the workmanship of God, speaking against their own salvation, becoming their own bitterest accusers, and being false witnesses [against themselves]. Yet, reluctant as they may be, these men shall one day rise again in the flesh, to confess the power of Him who raises them from the dead; but they shall not be numbered among the righteous on account of their unbelief.
2. Since, therefore, it is a complex and multiform task to detect and convict all the heretics, and since our design is to reply to them all according to their special characters, we have judged it necessary, first of all, to give an account of their source and root, in order that, by getting a knowledge of their most exalted Bythus, you may understand the nature of the tree which has produced such fruits.
Source: Adversus haereses (New Advent)