Mandatory to use Repository pattern

No. Repository pattern is not mandatory.

But it is really useful in complex projects and/or if you want to use unit testing. Read this article: http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application[^]

But it is not between the view and the BL, it is between the data model and the controller. And it is not only (not really?) an abstraction layer, it is a way to separate the logic from the data, so you can change the data source easily - for example in a mocking scenario.