Healing Grace
Two effects on one white mana, and the pairing is the design idea: bundle a small damage shield with an equal chunk of lifegain so a single tap answers a threat and pads attrition math at once. The prevention clause is the flexible half; naming a source of your choice lets it blunt a burn spell to the face, blank a damage-based removal effect aimed at a key creature, or tilt a combat trade in your favor. The lifegain rides along, so against a lone burn spell or an unblocked attacker the swing reaches six points across both halves. But the whole spell hangs on a single target: if that target becomes illegal before resolution (the creature it was protecting dies in response, say), the spell fizzles entirely, and you gain nothing. There is no consolation life. That fragility is worth weighing against a pure shield like Holy Day or a straight lifegain instant, both of which are harder to strand. The deeper limit is generational: point-source damage prevention was tuned for an era when threats arrived one big swing at a time, and the profiles that came to dominate later (multiple attackers, instant-speed reach, sacrifice-fueled drain) route around a three-point cap on one source. Clean, literal white defensive design that asks you to find the exact turn where stopping one source is enough, and to make sure the target survives long enough to matter.

