Plus, it doesn't remove itself from the game so you can get it back with Regrowth, Yawgmoth's Will, and other graveyard recursion cards (including Gaea's Blessing, further down on this list)
These enter the battlefield untapped and allow you to tap, sacrifice and pay 1 life (at instant speed) to search your library for a land card with the one of the two land types written on them
The Flame of Keld is a card that is great to gain back some card advantage and is a great addition out of the sideboard in certain matchups
That puts it into an unusual situation of impacting the board and killing someone at the same time, which is very important when dialing it up against multiple players
This can be used to enable various potent effects, it can also notably allow you to sneak powerful infect creatures and the likes of Phage, the Untouchable through an opponent's defenses undeterred