"mahayanas and theravadins are so very different on their views of samsara, that some people argue they are effectively two different religions"
Within Buddhism there are two major traditions, the Theravada and Mahayana and while both have much in common they also have different approaches and emphasas. They have some differences from one another in how they see Samsara functioning in which some argue they are two completely different religions.
The word Mahayana means 'great vehicle'. It is called this because it has so many different forms that one is bound to suit everyone, therefore all can find a space in this vehicle that carries us to salvation or liberation from Samsara. However the word Theravada means 'small vehicle' and this is meant to call our attention to the fact that Theravada seems more concerned with the monk's salvation than with that of the laity. Therefore it carries less people to salvation because it only has one possible route.
The most important virtue in the Mahayana in compassion for others. All forms of teachings and practice are for the welfare of others caught by the curse of samsara. This is at the heart of ideas like the Bodhisattvas and Heavenly buddhas…beings who are moved by compassion for others and act to save them if the central virtue of the Mahayana is Karuna then the goal is to get as many as possible to achieve enlightenment, and to do this different paths are on offer. However the central virtue of the Theravada is prajna or wisdom. The theravada monks achieves for himself alone, the only assistance that be given to another being is through teaching , example and encouragement - no gods or men can help the Theravada monk on the path to englightment.
There is a further way in which approaches to Samsara differ between Theravada and Mahayana. In the Theravada view Samsara and Nibbana are complete opposites. Samsara is seen as the enemy to overcome and nibbana is seen as the 'prize' to those who overcome...