Oneness of mind or “like-mindedness,” obviously means to be thinking the same thing, to be in agreement, to be unanimous in thought (from “unun” – one, and “animus” – mind). The New Testament constantly exhorts believers to be of one mind (Philippians 2:2), to be in agreement (2 Corinthians 13:11), and to live in harmony (Romans 12:16).
Perhaps the basic answer to your question can found in St. Paul’s letter to the Romans as he proclaims that all of us should live “in accord with Jesus Christ.” (Romans 15:5)
When it comes to linear measurement, there needs to be a standard. Could we ever know the length of something if everyone decided for themselves how many inches are in a foot? We might all have our own ideas about measurements, but thankfully there is an exact standard so that all of us can be in agreement as to the length of an inch, a foot and a yard. These standards are set by the National Bureau of Standards in Washington DC. However, when it comes to how we, as Christians, should think and act, Jesus Christ, Himself, is our Standard. If we are to be of one mind, then we must have His mind. Our way of thinking must line up with Christ’s way of thought; and His thinking is revealed to us in God’s Word.
All Christians, therefore, must agree with Christ. If I disagree with Christ or if you disagree with Christ or if we both disagree with Christ, then we are not of one mind; and what value is there if we agree with each other, but disagree with God’s standard? Therefore, Christ’s Church must make every effort to align with Jesus and His Word. We must love what He loves, hate what He hates, and think as He thinks. In the days of the Early Church, a believer would have been completely out of place if he were not in agreement with Christ and His Word; should this be any different today? Did the Gospel change? Does Christ change? Of course not!
Even though we are many, we are to be as ONE BODY. Even though we have many minds, we are to have ONE MIND. Even though we have many mouths, we are to be as ONE VOICE: united together in Spirit – worshiping, praising, and glorifying God.