Straight from the Pope's mouth

[Belacqua]

Dante made up what today would be a sci fi story of hell. There is a lot in his Inferno that never existed before, in the RCCs BS. He wasn't a member of the clergy, unless you can show me differently.

I suspect that "sci fi" may be a bit of an anachronism. He was working in an old allegorical tradition, of which he produced by far the greatest work in that genre.

And of course he didn't write only about hell. The two thirds on Purgatory and Heaven are far more beautiful and fascinating. 

But you're right that he was not writing prophecy or scripture. Nor was he a clergyman. He did write fiction which dramatizes and symbolizes Christian theology, particularly that of Thomas Aquinas. The structure and symbolism of the poem make difficult theology much more accessible.

Of course he made up characters or imagined events which are fictional, but in every case these serve to clarify the theology.

It's generally agreed that in those passages where his symbolism differs from Aquinas, this is done for poetic reasons, to depict things which, according to standard theology, would not be visible to embodied humans. Showing heaven as having spatial extension, for example, is incompatible with Catholic views of what heaven is like. But Dante is careful to remind us, over and over, that the character he's portraying has been granted special privileges, and visions of symbols, so he can go back and report. Near the end of the Paradiso he uses the ineffibility topos so often that we really can't miss the fact that what he's telling us is a poetic approximation to something that can't be verbalized.

Popes Julius II and Leo X didn't hesitate to acknowledge Dante's greatness, when they designed the program for Raphael's masterpiece the Stanza Della Stegnatura, a group of frescoes honoring the very greatest of those who contributed to Western knowledge. He is the only figure to be portrayed twice in these frescoes -- once in the literature section and once in the theology section.