by virtue of one's office; in the nature of one's duties
Used when an action is taken or a statement is made because of one's official position or role, often implying it is not a personal matter.
By virtue of my position, I had no choice but to attend that meeting.
In the nature of his duties, he is obligated to disclose that information.
Compound of 役目 (role, duty) and 柄 (character, nature). The exact historical derivation is uncertain, but the combination conveys 'by the nature of one's role'.