QUESTION: What is specific to the Amidist approach to the nembutsu that might distinguish it from the approach of other similar schools?
SHORT ANSWER: Nothing
LONG ANSWER: Nembutsu is refuge. Taking refuge is the core mystical act that defines Buddhism. It is the only practice that all Buddhist schools have in common. To take refuge in one Buddha is to take refuge in all Buddhas. However, different Buddhas show different facets of Buddha Nature. Amida shows primarily the facet of all acceptance. Therefore Amida Buddha is a favourite Buddha for ordinary people. Pureland Buddhism derives from the Buddha's teachings directed to ordinary folk. We understand Pureland, therefore, to be an original form of Buddhism deriving from the earliest times. We, therefore, take refuge in Amida Buddha and we commonly do so using the formula "Namo Amida Bu." We do not see this as essentially different from any other form of taking refuge such as may be practised in any school of Buddhism.
However, while there is no difference in essence, there are differences in style and focus. The emphasis, when one takes refuge in Amida, is upon acknowledgement that the being who seeks refuge needs to do so because of being a "foolish being of wayward passion", a vulnerable, limited, deluded, error-prone mortal. Here, therefore, there is a recognition that we each manifest greed, hate, pride, worry, sloth, and a wide variety of forms of self-centredness and that, although we might improve in some areas, the fundamental propensity to give rise to such characteristics is indelible and we are, therefore, incapable of achieving our own salvation by our own self-directed efforts. This recognition adds extra power and urgency to the urge to take refuge. Taking refuge comes to have the sense of turning to a salvific power that we ourselves lack.
In this act of taking refuge, therefore, there is a profound sense of letting go and of relief. We see the self-perfection project to lie in ruin, but we also feel a great gratitude for the presence and support of the Buddha who sees us in our actual state and loves us just so, even as we are. This is deeply moving. Our Amida form of nembutsu, therefore, is a devotional and emotional practice, something that touches the heart and that links together all those who are similarly moved. This linking generates a sense of community and fellowship. Amidist practice, therefore, is often more communal, singing together rather than sitting in isolated silence. There is a place for solitude and silent contemplation, but I am pointing out here a difference of emphasis in style. Reciting the nembutsu together we not only take refuge in the Buddha but find refuge in the sangha in a palpable sense too.
Fundamentally, therefore, nembutsu is refuge and refuge is Buddhism, and Amida Buddhism merely asserts this basic faith. In style our practice is less perfectionist, more devotional, more communal, and more emotional and it has its own distinctive ways of understanding core Buddhist teachings in accord with this orientation.
The Buddha, Dharma and Sangha are, of course, the objects of refuge so inevitably important, though it is worth noting that the first ever Buddhists did not take refuge in sangha because at that stage there wasn't one. I'm not sure that "study" of karma is essential - more a taken for granted assumption. Doing practice on behalf of all sentient beings is certainly not universal. Plenty of Buddhists have done their practice simply with a view to individual salvation and have regarded the salvation of others as their own affair. Of course, the great teachings - Four Truths, Dependent origination, Factors of Enlightenment and so on are available for anybody who is interested to delve into, but one can be a Buddhist without them or without any particular group of them. Different schools have different emphases. All this, however, is to answer the point pragmatically. The point of my original posting is to say that Pureland traditionally has the attitude that "only nembutsu is real and true" so that in those schools, nothing else is required, or, to put it the way that we would in Amida-shu, everything else is implied therein and so may but need not be unpacked from it. Namo Amida Bu.