I think the basic difference between theological fundamentalists and theological liberals can be summed up this way: fundamentalists think everything is a first order issue while liberals think nothing is. This is why fundamentalists have often been described as Evangelicals who are constantly angry about something. Just about everything, so far as the fundamentalist is concerned, is a first order issue worthy of separation.
Liberals, by contrast, see almost nothing as a matter for separation. Deny the resurrection if you will, but this surely just amounts to a different view among many. Reject the deity of Christ, no matter. We can find a way to co-exist together. You name it, liberals will view the matter as little more than a different opinion, probably of equal validity to any other. There are almost no grounds worthy of separation.
Of course, most Evangelicals would want to see themselves as holding the balanced centre here. Which is nice for us, isn’t it! Evangelicals – at least for the most part – recognise there are some issues that are so serious they make genuine fellowship impossible. But they also recognise that this is not all, or even most, issues. For the most part, there are issues that we can disagree over and maintain fellowship with other believers.
The big issue for Evangelicals is knowing exactly where those boundaries lie. When is an issue so serious we need to break fellowship? When is an issue not so significant and we can happily disagree as brothers and sisters in Christ? These things can be difficult to discern.
And let’s not ignore the fact that sitting in the centre ground on this, so to speak, Evangelicals will have those in their ranks who push towards fundamentalism and those who lean towards liberalism. Not to say they are fundamentalist or liberal, just to say there will be a squishy boundary at both ends where Evangelicalism bleeds into those other categories. Some Evangelicals are more inclined to a separatism while others will have more of a unifying inclination. Some will insist as first order issues things that others view differently while others will insist on a unity which makes others baulk because it crosses a line that they deem first order. There is no Evangelical agreement across the board on where all these things lie.
We have to try and be clear in our own minds which issues are clearly gospel matters and which are second or third order matters. To insist that there are no first order matters is to stand with the liberals; to insist that there are only first order matters is to be a fundamentalist. Evangelicals need to think carefully about where these boundaries lie in order to maintain their theological integrity.