Not every aspect of an essay's argument needs to be explicitly stated, since if you did try to do this, you'd probably never finish writing it. Experienced writers are able to distinguish between material which is essential for the reader to be able to relate the argument to a context, such as the academic field, and material which only needs to be hinted at, because readers can safely be left to work out the implications for themselves.
In the course of reading an essay, readers inevitably make predictions to themselves about where the essay is going to end up, so it is important that you show awareness of your reader's potential response to your writing either by confirming these predictions, or showing why they are inappropriate to the particular argument you're making. These predictions will be based on the context provided by the academic field and by the secondary literature from which you take quotations and to which you provide references, so that explicitly discussing the use you're making of these sources will help your reader know what to expect.
Setting out the key issues involved in your approach to the question in the introduction to the essay is a way of recruiting the reader's inferences onto your side of the argument, as is providing signposting at a later stage of the essay.