Sometimes my co-religionists (Baha'is) describe the concept of progressive revelation as an idea that humanity is culturally evolving, and is able to handle certain forms of truth and teachings at different times appropriate to the sophistication of society and general intelligence levels. Thus, the oldest levels are good enough when people live simple lives, and then religion became more sophisticated with very ancient Hinduism and Judaism when people settled in cities, and then Christianity and Buddhism came along when there were empires and very complex societies, and then Islam came along with national identity and more sophisticated science, and the Baha'i Revelation is most appropriate now, and is a religion suitable for a time when everyone is literate, and many are scientifically trained, and the world is being united by technologies of transport and communication. In essence, earlier religions are like grades in K-12 and the Baha'i Faith is like college.
I don't like that way of describing Progressive Revelation. One problem with it is that there are many simplistic and foolish thinkers in the "more advanced" religions just as there are many very sophisticated, wise, and mature teachings in some of our oldest religions.
Today I was reading John Polkinghorne's recent (2011) book Science and Religion in Quest of Truth. He makes a nice point about how one uses various sorts of sciences and even different aspects of physics to understand the whole natural work. We scientists suppose there is some sort of an objective reality lying beyond us, and this is glimpsed through our scientific techniques, reading instruments and measurements, applying mathematics and logic, requiring testing and verification, peer review, and so forth. We use Newtonian physics for some things, and Relativity or Quantum physics for other things, and we use Biology, Chemistry, Geology, and so forth for understanding various aspects of reality. I'm a social scientist, so I have a lot of problems with background that natural scientists don't have in the same degree, but it's all essentially the same process.
I think it would be more accurate if Baha'is used this sort of idea as a metaphor for Progressive Revelation. Just as various forms of science help us understand reality and truth, the various religions and their traditions and scriptures help us understand how people have tried to understand and worship God. A person who wants to understand how nature works needs to study Chemistry, Physics, Biology, and so forth. Psychology, Sociology, Linguistics, Anthropology, and Medicine are also useful sciences to gain insights. A person who wants to understand God ought to study scripture, theology, the sociology of religion, doctrines, community life within various congregations, religious history, and so forth, and also ought to investigate Islam, Christianity, Hinduism, various new Religions Movements, and that sort thing. The scriptures and teachings of all religions may contradict each other sometimes because religions are vulnerable to people imposing their own flawed understanding on things (much more than science, but science has this problem too). In other cases where religions seem illogical or contradictory, it may be a case like particle-light duality or quantum physics or imaginary numbers in mathematics, where the nature of reality itself is not the sort of thing easily grasped by our minds.
In essence, the Baha'i Faith is this recognition that all the various religions and their approaches to God and Truth ought to be embraced and incorporated, just as science and the scientific method (rational thought, the human intellect) must also be applied if we are to find God and adequately Worship and "know" God. The Baha'i Faith offers a framework in which we can integrate the religions and sciences into a whole, and as part of this framework, the Baha'i Revelation offers scriptures and social teachings that represent some of the latest or most recent Revelation materials we've received.
So, studying the Baha'i Faith and embracing Baha'u'llah is something like keeping up with the latest scientific journals across multiple scientific disciplines, while remaining within one of the older religions is like specializing in a particular discipline and remaining focused on significant works that took place a while back. There is nothing necessarily wrong or "less sophisticated" about this. I enjoy reading Darwin, Feymann's lectures, essays by Lewis Thomas, Rene Dubois, Richard Dawkins, E.O. Wilson, Konrad Lorenz, Gregory Bateson, and so forth, but the fact that I prefer reading mostly life scientists does not mean I think sociologists or chemists are wrong or less significant, and the fact that I am particularly fond of a bunch of people who mostly wrote between the 1950s and 1990s doesn't mean I have made a bad choice. Maybe I just like the style of someone like Loren Eiseley or Rachel Carson more than the style of whoever is the more recent scientific writer or essayist. Yes, much of what these people wrote about is dated, but quite a bit of it transcends time and catches the beautiful essence of science anyway.
And so we have people who prefer Orthodox Christianity or a particular school of Sufi teachings within a Shia Islam tradition, or Tantric approaches to Shiva in Hinduism, or the Dalai Lama's Tibetan style of Buddhism or the "Japanese Protestantism" of Genku and Shinran. . . it's just like different sorts of scientists and different sorts of studies or experiments. Whether it's religion or it's science, it's all part of a search for Truth.