God is by definition the Supreme Being. If one admits to a ranking of the powers or status of Persons, for example by saying that the Father is truly God, while the Son only has some God-like qualities, then immediately the Trinity collapses, and the result is a Unitarian or Arian heresy. Hence it is essential that the three Persons in the Godhead be absolutely equal in divine nature and power.
"Therefore we condemn the Jews and Mohammedans, and all those who blaspheme that sacred and adorable Trinity. We also condemn all heresies and heretics who teach that the Son and Holy Spirit are God in name only, and that there is something created and subservient, or subordinate to another in the Trinity, and that there is something unequal in it, a greater or a less, something corporeal or corporeally conceived, something different with respect to character or will, something mixed or solitary, as if the Son and Holy Spirit were the affections and properties of one God the Father, as the Monarchians, Novatians, Praxeas, Patripassians, Sabellius, Paul of Samosata, Aetius, Macedonius, Anthropomorphites, Arius, and such like, have taught." (Second Helvetic Confession, Chapter 3, 1566).