Abstract: This study aims to interpret the essence of the spirit of the Fourth Plenary Session of the 20th Central Committee of the Communist Party of China from a philosophical perspective. First, it clarifies the historical positioning of the 15th Five-Year Plan period (2026–2030) as a crucial stage connecting the past and the future in basically realizing socialist modernization, and dialectically analyzes the current complex and intricate international situation based on Marxist historical materialism. Second, it puts forward that the broad historical era defined by Marxism remains "unchanged," while capitalism has undergone "profound changes." Finally, it discusses the continuity between the worldview and methodology of Xi Jinping Thought on Socialism with Chinese Characteristics for a New Era and Marxist philosophy, emphasizing the dialectical unity of worldview and methodology. It concludes that the key to fully implementing the spirit of the plenary session lies in mastering the worldview and methodology of Xi Jinping Thought on Socialism with Chinese Characteristics for a New Era.