AJANI! What a beloved dude. I love his vengeance flavor, so I keyed off of that for my redesign.
First ability: I wanted to do Vengeance as one of his abilities for his vengeance flavor, but Gideon Jura already blatantly has that effect as one of his abilities. So, I opted for a variation that was both red and white. I noticed that Chandra, the Firebrand was able to deal 1 damage to creatures as a +1 at four mana. So, taking that into account, I figured 2 damage to tapped creatures as a +1 was fair. But, to be safe, Ajani also now costs five mana.
Second ability: Resurrection is a white thing. Haste is a red thing. Put them together, and you get a potent combination. This plays into the vengeance feel in that something is coming back around a second time but even fiercer than before (haste).
Third ability: I wanted your burn spells and life gain spells to be able to become one or the other. But then I discovered there wasn't enough space for the text of this kind of ability. However, that's when I realized that only being able to turn your life gain spells into damage spells is a flavor win since Ajani's previous card was the monowhite life-gaining one. This "ultimate" ability reflects the mechanical change for this red-white card.
Though, I "read somewhere," that Ajani Goldmane is actually the result of Ajani AFTER he has calmed down with his vengeance thing. But that's all right.
Also, emblems haven't been invented, yet - so that's why there's that "for the rest of the game" clause.