Ratzinger's 1997 interview with journalist Peter Seewald, which was published as a book entitled Salt of the Earth, is a fascinating window into the mind of this remarkable believer and thinker. Here's an excerpt in which he answers some questions about Christianity in relation to the other world religions:

All the great cultures we know of had or have religion as the most important thing in common. It seems that there is sort of a unison of doctrines, for example, in the exhortation to moderation, the warning against egotism and autonomy. So then why shouldn’t all religions be the same? Why should the God of the Christians be better than say, the God of the Indians? And why should there be only one religion that confers true bliss?

This proposal, which has been made since the early days of the science of comparative religions in the Enlightenment (though it had come up even before that), is already self-contradictory with respect to the religions themselves, for these are plainly not the same. There are various levels [of religion], and there are religions that are obviously sick, religions that can also be destructive for man.

The Marxist critique of religion is correct insofar as there are religions and religious practices that alienate man from himself. As an example, let us think of the fact that in Africa belief in spirits continues to be a great obstacle to the development of the land and to the construction of a modern economic organization. If I constantly have to protect myself against spirits, and an irrational fear governs my whole sense of life, then I am not rightly living what a religion at its depth should be. And so we can also see that in the Indian religious cosmos ("Hinduism" is a rather misleading designation for a multiplicity of religions) there are very different forms: very high and pure ones that are marked by the idea of love, but also wholly gruesome ones that include ritual murder.

We know that human sacrifices shape a portion of the history of religion in a terrible way. We know that political religion has become an instrument of destruction and oppression; there are, as we know, pathologies in the Christian religion itself. Witch burning is a recrudescense of Germanic customs. It had, with difficulty, been overcome by the early medieval missionaries, and then it reemerged in the late Middle Ages as the faith began to grow weak. In a word, even the gods are not all alike; there are decidedly negative divine figures, whether we think of the Greek or, for example, the Indian religious cosmos. The idea that all religions are equal is already disproved by the simple fact of the history of religion.

But could we not also accept that someone could be saved through a faith other than the Catholic?

Well that’s a different question altogether. It is definitively possible for someone to receive from his religion directives that help him become a pure person, which also, if you want to use the word, help him to please God and reach salvation. This is not at all excluded by what I said; on the contrary, this undoubtedly happens on a large scale. It is just that it would be misguided to deduce that from this fact that the religions themselves all stand in simple equality to one another, as in one big concert, one big symphony in which ultimately all mean the same thing.

Religions can also make it harder for man to be good. This can happen even in Christianity because of false ways of living the Christian reality, sectarian deformations, and so forth. In this sense, in the history and universe of religions, there is always a great necessity to purify religion so that it does not become an obstacle to the right relation to God but in fact puts man on the right path.

I would say that if Christianity, appealing to the figure of Christ, has claimed to be the true religion among the religions of history, this means [in connection with what I just said] that in the figure of Christ the truly purifying power has appeared out of the Word of God. Christians do not necessarily always live this power well and as they should, but it furnishes the criterion and the orientation for the purifications that are indispensable for keeping religion from becoming a system of oppression and alienation, so that it may really become a way for man to God and to himself.