These are two cards expected to have an immediate impact in the all-common Pauper format. Burning-Tree Emissary is a solid value creature that essentially pays for itself by giving you one Red and one Green mana when he enters the battlefield. This should help speed up some of the Aggro and "Stompy" decks in the format. Casting him and potentially two other one-mana creatures in a turn is a huge tempo swing. Also, while Pauper already has premier burn spells in Lightning Bolt and Lava Spike, among others, Magma Jet will probably see play in decks that value the Scry 2, such as Izzet Delver, a top deck in the format.
Kudos to Wizards for making these two very useful cards more readily available and even eligible in Pauper!