You don't "play Xbox Live"—you use Xbox Live (now Xbox Network) as the service layer that enables online multiplayer, identity, and entitlements on Xbox consoles.
Your internet provider connects you to the *internet*. Xbox Network connects you to *Xbox's gaming ecosystem*—matchmaking, parties, licenses, cloud. Without it, your console can reach the internet but not Xbox's curated multiplayer fabric.
Xbox Network = the pipes. Game Pass Core/Ultimate = the ticket. Free-to-play = open gate.