It is very common to use reading or listening texts to introduce new vocabulary or grammar. This is a great way to introduce new language because it helps integrate skills and, most importantly, provides a context for the new language. Context is so important because it is this that gives the new language meaning and helps convey its proper usage.
Something that I often see teachers do, however, is give the students a text and have them immediately examine the text for the new vocabulary or the grammar. Something I always advise them to do is set a reading or listening comprehension task first. The students then have a purpose for reading/ listening and most importantly are focused on the meaning first. This is important for a couple of reasons. Firstly, students want to make meaning of it. We read and listen to things to get meaning from them. So even though the teacher might have the learners answering questions focusing on new target language, the students will naturally want to focus on what the meaning is. Secondly, by having the students answer a comprehension question (or questions), the teacher can assess (and ensure, through checking the answer) that the students have understood the text. This is essential, because the text is the context – and the context gives the vocabulary or grammar meaning. If the students haven’t understood the context, then they can’t understand the new vocabulary or grammar.
So always set a comprehension task first. Then when you are sure that the students have understood it, they can start to look at the new language that you are using the text to introduce.