One will allow you to deal a powerful alpha strike with your vigilant creatures with flying and double strike, while the other mode will grant your creatures lifelink and protection
Your ability to open packs meanwhile is governed by a 12-hour timer, which you can accelerate with an in-game currency called Pack Hourglasses, and given the level of rarity of different cards - and the scarcity of packs - that means collecting 'em all is going to take a very, very long time
Whether its with a return of Eldrazi or something else, or maybe just making colorless evergreen, Oath will forever change the future of Magic thanks to that step
It prevented your creatures from getting exiled from an Anger of the Gods while attacking the game from another axis
For each copy sold, Wizards of the Coast has pledged to donate $30 to Extra Life
Signaling is a complicated concept, and an in-depth discussion is a topic for another time (but see Marshall Sutcliffe's "Signals")