The ones that are most common are the topics of homosexuality (I've dealt with the obscurity of this discussion in the past) and that of post-mortem retribution (the doctrine of hell).
When I was an undergraduate student at Azusa Pacific University, studying Theology and Biblical Studies, I decided to construct an independent study course on the doctrine of hell with Dr. Denis Okholm. I thought it would be good for me to know how hell works, but I wasn't expecting all that complex a discussion. I supposed that I would come out with stronger and more decisive exegetical and theological arguments against universalism. But what I encountered when I began my research was more than I had bargained for. It took little time for me to realize that where I had assumed there was such clarity, there was actually much obscurity. (This might be a good time for me to mention that my thoughts on this topic are by no means reflective of Dr. Okholm's or APU's position on these matters). For every Biblical passage I found that spoke of retribution, punishment, or destruction, I was challenged as well by passages which spoke of the universality of God's grace and salvation. Where the Bible speaks of "whipping and gnashing of teeth," it also says things like, "[God] wants all people to be saved and to come to a knowledge of the truth. For there is one God and one mediator between God and mankind, the man Christ Jesus, who gave himself as a ransom for all people" (1 Tim. 2:4-6). There are a lot of "all" passages which seem to contradict all the "many," "some," or even "few" passages. For every credible theologian I found who argued for eternal damnation, I found a surprising number of others who at least wrestled with the simplicity of the matter (even including evangelicals like John Stott and J.I. Packer), even those who argued for universalism or some softer version thereof (I think Jurgen Moltmann might fit this category, at least when he speaks of Christian ethics). I was obviously in over my head. And, unfortunately, I thought I had to come to some decisive decision on the matter (so I chose to support annihilationism... at least then, everyone who remained would be saved... that almost like saying "all").
"The proclamation of the Church must make allowance for this freedom of grace. Apokatastasis Panton [meaning universal salvation]? No, for a grace which automatically would ultimately have to embrace each and every one would certainly not be free grace. It surely would not be God's grace. But would it be God's free grace if we could absolutely deny that it could do that? Has Christ been sacrificed only for our sins? Has he not ... been sacrificed for the whole world? ... [Thus] the freedom of grace is preserved on both these sides."In other words, we can't limit God's grace on either side, either by saying that God 'must' save everyone or that God 'can't' save everyone--even those in hell.
He also wrote,
"If we are certainly forbidden to count on this [universal salvation] as though we had a claim on it, as though no possible claim, we are surely commanded the more definitely to hope and pray for it as we may do already on this side of this final possibility, i.e., to hope and pray cautiously and yet distinctly that, in spite of everything which may seem quite conclusively to proclaim the opposite, His compassion should not fail, and that in accordance with His mercy which is “new every morning” He “will not cast off for ever” (La. 3:22f., 31)."In other words, if we can't count on universalism, if we should be careful not to be too decisive on the matter, then we should still be able to hope for it. We should be rooting for God to save everyone, since everyone is an object of God's love. Many will reject this with anxiety. Barth's response might be,
"Strange Christianity, whose most pressing anxiety seems to be that God's grace might prove to be all too free... that hell, instead of being populated with so many people, might some day prove to be empty!"Let's not stress out if God ends up saving everyone... I think it's Biblical, in fact, to be excited by this possibility.
If I've learned one thing over the years--of which I've spent much time reading and thinking about the doctrine of hell and the Biblical concern for salvation--I have learned that the Bible does not indulge our desire for neatly packaged answers. We find ourselves caught in the tension of God's freedom. The Bible has its moments of clarity on both sides of the issue, which leaves us in obscurity. When something is left so obscure to us, it's likely that it's not for us to know. It may not be our job to know who's in and who's out. It may simply be our job, with all our lives, to witness to the crucified and resurrected Christ whether hell is eternal or not.
So if you think you have found the definitive passage on the subject, if you think you've sorted out the matter, if you have found yourself saying, "the bible clearly teaches..." regarding the doctrine of hell, then think again. And consider what's really most important. "While we were still sinners, Christ died for us."
So, as I've said before, I'm not sure if I can be a universalist, but I sure hope that God is! I believe that where there is not biblical certainty, there is most certainly biblical hope.