Paragraphs are parts of overall discourse, informed by the strategies a writer chooses for the overall piece. Effective writers think in terms if paragraphs, whereas less skilled writers think in terms of sentences and even more less skilled writers think in terms of words. LeClerq says that just as the whole text requires a thesis statement, a paragraph requires a topic sentence. Topic sentences introduce the idea within the paragraph. Topic sentences set the boundaries for the paragraph.
Topic sentences help ties paragraphs together through the use of transitions.
LeClerq says that effective topic sentences need cueing transitions to help the reader keep on track. In a multi-paragraph text, you should be able to identify the topic sentence of each paragraph. Read separately, the topic sentences should inform the reader of each step of an analysis. Then examine the coherence of the topic sentences as they relate to the overall thesis set-up by seeing whether the topic sentences form a coherent paragraph.