The main function of an Ethernet switch is to connect multiple devices within a local area network (LAN) and facilitate communication between them. It receives incoming data packets and redirects them to the correct destination device based on its MAC address. By creating separate collision domains for each connected device, switches enhance network performance and efficiency. Ethernet switches operate at the data link layer of the OSI model, allowing for faster data transfer and reduced network congestion compared to traditional hubs, making them essential for modern networking.