Book VII. The Arians are adepts at concealing their meaning; at the use of Scripture terms in unscriptural senses (§ 1). They have already been refuted by the proof that Christ is the true and coeternal Son; and Hilary now advances to the proof of the true Divinity of Christ, which is logically inseparable from His true Sonship (§ 2). But the danger is great lest, in attacking one heresy, he should use language which would sanction others (§ 3). Yet the truth is one, while heresies are manifold.
Each of them can be trusted to demolish the others, while none can establish its own case. He illustrates this by the mutually destructive arguments of Sabellius, Arius and Photinus (§§ 5-7). Christ is proved to be God by the name God which is given Him in Scripture: The Word was God (§§ 8, 9). The name is His in the strict sense, and not any derivative meaning (§§ 10, 11). Yet Father and Son are not two, but one God (§ 13). Being the Son of God, He has the nature of God, and therefore is God (§§ 14-17), and yet not one Person with the Father (§ 18).
Again, His power, manifested in His works, proves His Godhead (§ 19), as does the fact that all judgment has been given Him by the Father (§ 20). Christ's own words display the truth (§ 21). The Arians are blind to the plain sense of Scripture, and are more blasphemous than the Jews; Christ's reply to the latter meets the objections of the former (§§ 22-24). He asserts His unity with the Father (§ 25), and makes His works the proof (§ 26). The Father is in the Son and the Son is in the Father (§ 27): this is illustrated by the transmission of physical properties from parent to child and from flame to flame (§§ 28-30).
In fact, the Catholic is the only rational explanation of the words of Scripture (§§ 31, 32). Again (§§ 33-38), the way to the Father is through the Son, and knowledge of the Son is knowledge of the Father. This would be impossible, were not the Son God in the same sense in which the Father is God. Thus the contrary doctrines of Sabellius and of Arius are confuted; there is neither one Person, nor yet two Gods (§§ 39, 40). Christ calls upon us to believe the truth, and belief is not only possible but reasonable (§ 41).
Source: On the Trinity (New Advent)