What are our biblical grounds to divide with any true brother in Christ over doctrinal distinctives, no matter how biblical they may be?What follows, with minor adjustments, is my answer:
The question I really have to ask first is, "What do you mean by 'divide'?" I do not believe myself "divided" from even though we are not a part of the same local church or denomination and probably could not be. I'm afraid this is simply a reality in a sin-broken world where even the elect are not yet perfected. Yes, there is a division of sorts on the administrative level of our fellowship, but not one that keeps us from recognizing one another as brothers and working together in the Kingdom.
Is there biblical justification for this? Not really, at least not in the sense of a statement that says, "This is how things are supposed to be." It is simply an unfortunate reality -- and one that is insurmountable at the present time for a number of reasons
(1) Because none of us are untouched in our ability to 'reason' due to the fall, none of us sees the Bible with perfect clarity. For that reason we cannot agree completely on some very important, though non-essential to salvation, issues. Baptism is a great example, and so is the nature of plural leadership in the church, the calvinist/arminian divide, how to organize for missions etc, etc. "How can two walk together unless they be agreed?" Such differences of opinion make it all but impossible for all true Christians to fellowship and serve in the same local body. This is a very sad admission, but one that is true and has been true for 2000 years! Remember Barnabas and Paul? We could add Peter and Paul in Galatians (at least for a time), etc. And then add to the fact that it is possible even for genuine Christians to fall into grievous error, the end result is external division on the local level.
(2) Some would say, "Well then, we should not ever make an issue of such non-essential matters." As wonderful as that sounds, it ends up with a disastrous outcome. The only way to do that is to reduce down to a "least common denominator" approach to a local church's confession and practice. "We will only stand on those issues about which all can be agreed." Because the dividing line between what is essential and non-essential is in some places a bit fuzzy to us; and because that line will be drawn in different places by different people (due to the problem discussed in #1), you ultimately end up with a Methodist church -- all-inclusive but totally compromised. You see this happening right now in the discussion between some Protestants and the Roman Catholic church (you also saw it in the old "ecumenical movement") The desire for an outward appearance of institutional unity often leads to the willingness to discard much truth that is essential. Baptism is a great example. I believe firmly that baptism is a picture of an inward and spiritual reality and that Christ commands it to be accepted as an act of obedience upon a believer's public confession of faith in Him. To disregard that in order to make room for infant baptism -- since this is admittedly not an essential issue -- would to my understanding be a betrayal of the very purpose of baptism. I don't believe those who practice infant baptism are lost, but I do believe they are wrong. And I believe their practice will, of necessity, lead to the admission and acceptance of unregenerate church members -- and that is an essential issue since it tends to lead to a betrayal of biblical truth by the next generation! Therefore, I am constrained to "divide" with a brother over a non-essential, as far as local church membership is concerned. Yet, in the case of a faithful Presbyterian brother for example, I am united with him in all else and willingly and gladly work with him and fellowship with him on a number of levels beyond that of local church structure.
This brings me to ...
(3) The true church is united on the universal level, even where there is a necessary division on the local level. True biblical unity exists between all regenerate believers as they draw near to Christ. So even though I am not organizationally unified with every other believer on the planet, nevertheless a genuine union exists and can be seen in our fellowship when we meet, when we work together for the cause of Christ outside the local church structure, when we pray together, etc. And so, while we pray for a complete and unhindered unity at every level, we know that in a broken world this will never quite be the case organizationally. Therefore we act with unity and charity toward one another at ever level possible, and accept the unfortunate divisions that are necessary for the sake of conviction and truth in the mean time. You see, unless we are willing to compromise every principle outside of a very few basic statements of faith (and who would decide what those are?), this is the unfortunately necessity.
I hope this begins to help.
Well, to all who read this, keep thinking about this issue, and measuring it and your response to other believers against Scripture. May God give us a real and Christ-honoring unity!