In terms of authority, what is at the core of More's decision to remain faithful to his beliefs (according to A Man for All Seasons by Robert Bolt)?
More's final authority is God - as enotes states in the first link below, he "placed God's rule over that of the State". Even though he might have been willing to compromise his ethics as to the nature of what he was being called upon to swear to if he could "find a legal loophole to protect him", for him the act of taking an oath was absolute. Bolt says,
"More was a very orthodox Catholic and for him an oath was something perfectly specific; it was an invitation to God...to act as a witness, and to judge...the consequence of perjury was damnation" (Man for All Seasons, NY: Random House, 1962, p. xiii).
In a similar manner, the same hierarchy is true of More in a societal context. More was a man who was undeniably absorbed in the earthly British community in which he lived, but ultimately he viewed the state as "subservient to the larger society of the Church of Christ, founded by Christ...ruled by Heaven" (Bolt, p. xv - xvi).