Today is the day when Moments of Triumph come to Destiny 2 from the original game, and they are here to show you how much you progressed through the game. You also get rewards for basically playing Destiny 2 and that’s all, and by that, we mean completing certain missions. Why not get some extra loot for your effort? This is the best way to get some exclusive loot, and everyone can do it, so by completing more and more Triumphs, you get closer to your Moment of Triumph, which comes with great rewards. Some Triumphs are still hidden, but they will get revealed once Solstice of Heroes starts.
A lot of these are going to get accomplished easily, and you have a lot of them done if you progressed through the main storyline. The rewards include a Legendary Sparrow, a Legendary Ghost, and more. On their Bungie post they said:
From now through August 28, 2018, players are invited to complete various in-game objectives to earn progress toward Triumph Points, which will unlock unique rewards.What’s available today is just a taste of what’s to come with the Solstice of Heroes event, which will expand the list of Triumphs and rewards that players may earn. The complete list of Triumphs will become available in-game starting on July 31, 2018.