In "Word Focus" Glenn McClure writes:
The serious student of Scripture will often find himself confronted with the need for balance in applying the Bible to life situations. The opening line of our printed text today is a case in point. Without doubt Scripture demands that the sincere disciple of Christ take a firm stand for what is right (Jude 1:3). But in our lesson today the companion truth is emphasized, which is the requirement of unity in the Body of Christ. The text reads, “Be ye all of one mind,” or literally, “of one mind, united.” The exact form Peter used appears only here in Scripture. In Greek it is a compound word: the first word meaning “together,” and the second word meaning “mind or understanding.” In classical Greek it literally meant “to be of one mind, to have the same thoughts.” It was used of the unity of conspirators. It was also the word used to indicate that an issue was decided by “common consent.” Both thoughts and feelings were included in its meaning. The Church fathers used this word often. To them it meant “unity of mind, agreement, and concord.”
Source: Building Christian Relationships: Adult Teacher's Insights, page 64.