The term Peter uses is a composite of two Greek words, with one referring to patterns of thought (the same root as found in the earlier term “unity of mind”) and the other referring to humility. Humility is not a quality that people highly celebrate (aside from lip-service); our innate selfishness has us gravitate to pride and arrogance (and so insisting that we are right). But children of God have received so much from the Father without any contribution on their part (think only of the dynamics of being born again; no one births himself but all are born), so there is place in the heart (patterns of thought) of God’s children only for humility, never pride. So the attitude befitting the Christian when there is insufficient “unity of mind” is humility of mind. Pride of mind sabotages any compassion or sympathy for the brother with whom you are not on the same page.