Why is it that a devoted Christian can come up with bizarre interpretations of Scripture, while an unbelieving scholar can provide solid expositions of important passages?
One solution is the view that, everything else being equal, a believer's interpretation will be better than an unbeliever's. Thus, the accuracy of one's interpretation is affected by intellectual qualifications, acquired skills and exegetical experience, but it is also conceded that spirituality makes some kind of difference.
However, this reflects a nature/grace scheme and trivialises the work of the Spirit. It suggests that our reason, our natural gifts, and our humanly-developed skills take us thus far, then the Spirit gives us an additional little push. I'm too much of a Van Tilian to be happy with such an approach.