Let's call him/her L.
L is innocent, and idealistic. L is private and reserved. L is shy. L has longing - to achieve great things and succeed in L's chosen field. L is in the clergy - a scribe, a scholar, a monk/nun. L is fundamentally a follower rather than a leader. L is a favorite of his/her superiors. L is intelligent - brilliant, even - and inquisitive. L is serious. L is focused. L works hard. L is gentle. L is moral. L is gentrified. L has enjoyed privilege and doesn't understand how much it's affected his/her life. L keeps his/her head in a crisis.
L's great virtue is intellectual honesty. He/she can't lie to others and he/she can't lie to herself - not well, anyway.
L should be sympathetic. L has a devotion, not just to truth, but to reason - he/she wants people to be intelligent and to think clearly. L is never a hypocrite; L will never preach love and practice hate, for instance.
L is a protagonist. L is one of the primary mechanisms by which the reader uncovers the lie, because L discovers the inconsistencies and inadequacies of the lie, and won't shut up about them or leave them aside.
L's arc is one of finding courage. L is a good person, but L has a comfortable life which he/she will endanger if L practices his/her virtues. L will lose the esteem of his/her teachers and colleagues, will lose the comfort and privilege of his/her position, will have to stand on his/her own two feet and engage in a contest with the orthodoxy and its protectors over the lie. These are not things that are easy for L. Nonetheless, L feels they must be done - if only he/she can bring herself to do them.
EDIT: Some research for this character. Logic and theology and how they fit together. Formal and informal fallacies. New testament. Also, occurring to me that I need holy texts for the religion.