The significance of essay writing in the UPSC mains lies in its ability to assess a candidate's critical thinking, coherence, and argumentation skills. Essays allow candidates to express their understanding of complex issues, showcasing their analytical abilities and breadth of knowledge. A well-structured essay is crucial for attaining a good score, reflecting the candidate's thought process and clarity. Contextual awareness and the ability to connect disparate ideas can significantly enhance the overall impact of an essay in the examination.