The main purpose of using keywords in SEO (Search Engine Optimization) is to help search engines understand the content and topic of a web page, making it more likely to rank higher in search engine results pages (SERPs) for relevant queries. By incorporating relevant and popular keywords into the content, headings, meta descriptions, and URL structure of a web page, search engines can better match it to user searches, improving its visibility and organic traffic. However, it's important to use keywords naturally and avoid keyword stuffing or overoptimization, as this can negatively impact search engine rankings and user experience.