Being of the same mind, we have to think the same things.That's the way I was raised, and what I believed most of my life. But here I'd like to see if I can present a different perspective.
One of the passages for supporting this position is Philippians 2:2,5:
NKJV Philippians 2:2 fulfill my joy by being like-minded, having the same love, being of one accord, of one mind. ... 5 Let this mind be in you which was also in Christ Jesus....
This quote sounds like we are to "think the same things". But I believe that is going beyond what the passage actually says.
Looking at the broader context, particularly verses 6 and following, Paul is talking about an attitude, not a doctrinal stance. He's saying, "Humble yourselves; be a servant, like Christ was". He's saying, "Let nothing be done through selfish ambition or conceit" (v3), but to have an humble attitude that accepts the other guy.
He is not saying, in either verse, to "think the same things"; he's saying, in context, "get along with each other".
This follows the example which Jesus himself set in picking his apostles. He picked common laborer fishermen, and he picked an "I'm holier than thou" Pharisee, and he picked a couple of guerrilla-fighter zealots, and he picked a despised, hated, not-to-be-associated-with-at-any-cost-don't-even-touch-him "filthy scum" tax collector. As this disparate group spent time with and learned from Jesus, their ways of thinking began to get similar, but thinking the same thing was not the mark of discipleship; instead, the mark of discipleship was love for each other. He did not say, "You can't be my disciples until you all think alike." He told them:
NKJV John 13:35 By this all will know that you are My disciples, if you have love for one another.
We also see this from the first few decades of church history. In the beginning, only Law-keeping Jews were Christians. When non-Law-keeping Gentiles were invited into the church by God, the Jews who kept the Mosaic Law at first thought the Gentiles had to become converted Jews in the process of becoming Christians. Although several passages in Acts indicate this, it's plainly spelled out in chapter 15:
NKJV Acts 15:1 And certain men came down from Judea and taught the brethren, “Unless you are circumcised according to the custom of Moses, you cannot be saved.”
For several decades there were essentially two groups of believers within the church: the "Jews who have believed" which stressed the keeping of the law (Acts 21:21), and the "Gentiles who believe" (Acts 21:25), who did not need to keep the law, except for four specifics (Acts 21:25), to keep peace between the two groups.
These two groups were "like-minded" in that they got along with each other, but they were not "like-minded" in that they did not "think the same things".
We, in the 21st century, forget that God approved of two very different ways of thinking, divided into two very different groups, in His first-century church. By forgetting that scriptural lesson, we make the mistake of thinking that modern-day Christians can not have vastly different ways of thinking and doing things but must instead "think the same things". I daresay that if we had a Jewish church of Christ across the street from the church of Christ I attend, which stressed the keeping of the Mosaic Law (not for justification purposes but for cultural purposes), most of us at my congregation would dismiss them as non-Christians, and would have nothing to do with them except perhaps to try and "convert" them. God did not dismiss them; who are we to cause a division where God has not? Instead, we should be marked for being divisive in such a case (Rom 16:17).
I believe it's true that if we use the Bible as our standard, our thinking will more and more focus into thinking the same things, but I don't believe the Philippians 2 passage as quoted above can be used (in context) as a proof-text for that concept.
Neither can Romans 15:5-6 be used, in context, to support the idea that Christians must "think the same things". The passage says:
NKJV Rom 15:5 Now may the God of patience and comfort grant you to be like-minded toward one another, according to Christ Jesus, 6 that you may with one mind and one mouth glorify the God and Father of our Lord Jesus Christ.
Putting the passage back into its context, we find the next verse says that we are to "receive one another", not that we are to think like one another. The previous chapter makes this even more clear, in which we are taught that some Christians have no problem eating meat, whereas some do; some Christians observe special days as holy; some do not. But it's no matter that they don't "think the same things"; what matters is that each person has his own beliefs which are between himself and God (Rom 14:4,9,12), and that we are not to dispute over questionable matters (14:1 (even if one party feels the matter is not questionable)), and that we are to receive each other (14:1), pursue peace with one another (14:19), and to keep your own beliefs to yourself before God (14:22) rather than forcing them on the weaker brother.
(Some brothers might claim that people who celebrate Christmas as a "holy day", as Jesus' birthday, or Easter as a holy day, or, horrors! Passover, are not really Christians. But Paul makes it clear that observing holy days is not an issue (even if Christmas did start out as a pagan holiday, is not Biblical, and has nothing to do with the birth of Jesus); therefore we should not make it an issue.)
The point is that Rom 15:5 does not teach us to "think the same thoughts"; it teaches us to get along with and accept each other, even when we don't think the same thoughts on various issues.
Please do not get me wrong; I am not saying that anything goes; I am saying that these particular passages do not teach us to "think the same thoughts", and they should not be used as proof-texts for teaching that. To do so is to make them say what God has not said. I am also saying that God approved of much greater group differences in the first century church than many of us today will allow, and that the concept that we must "think the same things" is a man-made doctrine, not a Biblical one.