With seven mana, Golos, Tireless Pilgrim lets you cast three cards from the top of your library for free. That's great value, provided you can ramp to seven mana quickly enough and your deck is filled with big ol' spells for Golos to cheat out.
Thankfully, Golos, Tireless Pilgrim helps you with that first part. Assuming you hit your land drop the turn after you play Golos, you're set to start spamming spells. As for stacking the deck in your favor, you've got tons of powerful finishers like Blatant Thievery and Aminatou's Augury, as well as ways to chain Golos activations together like Early Harvest and Part the Waterveil. Pretty soon, Golos will be casting your entire deck for free, and from there it's up to you how you want to win.