" there's no art/ to find the mind's construction in the face/ he was a gentlemen on whom I built/ an absolute trust " - Phrase ' mind's construction ' a person's true thoughts and intentions cannot be accurately judged by their outward appearance. The phrase 'absolute trust' highlights Duncan's unwavering confidence in the former thane of Cawdor - the quote is significant as while Duncan focuses on the traitor being Macdonald the real traitor in the room is Macbeth and Duncan will almost regret putting his trust in him