Context is always an important aspect to consider whenever you analyse a text. Context refers to those particular elements of a situation that in some way or another affect the text (for example, the effects of time, place, ideology, social hierarchies, relationships, etc.).
Importantly, language has two potentially important contextual aspects: the context in which it was created and that in which it was interpreted. For example, a letter from a manager to one of his staff will be affected by context such as the situation itself, the power relationship that exists between the manager and the worker, the historical conditions and so on. Another example, when you speak to your parents or when you speak to a friend on the phone you will see that context naturally affects the linguistic choices - the style - of the discourse in important ways. Also see register.