Dante's view of salvation is rather complex, in keeping with the numerous strands of soteriology then operating in the world of medieval thought. (Soteriology is a branch of theology that deals with salvation.) The inherent ambiguity of Dante's position is exemplified by the apparently contradictory assertions of the Eagle in Paradiso XIX. The Eagle appears to be saying that divine justice is somehow beyond the understanding of human beings. This leaves open the possibility that salvation is possible for non-virtuous pagans like Virgil, Dante's guide and companion.
But then the Eagle immediately dashes such hopes by proclaiming that no human being has ever been saved who did not believe in Christ. And just to make matters even more complicated, the Eagle goes on to say that many of those who express faith in Christ will not be saved, whereas many who never knew him will be "eternally rich" by being saved. We seem to have turned full circle. Now it appears that virtuous pagans like Virgil can indeed be saved after all. But this simply raises further questions. Why hasn't Virgil been saved? Why is he still stuck in Limbo?
Dante's ambiguity is a reflection of contemporary theological debates. A number of medieval thinkers such as Thomas Aquinas believed that an individual could be saved despite only having implicit faith in Christ. In other words, those who'd lived before Christ, or those living in remote parts of the globe beyond the reach of Christendom, could still be saved through the free operation of divine grace. On this reading, it was both arrogant and presumptuous to dismiss out of hand the possibility of virtuous pagans being saved, as this would diminish God's power in effecting salvation.