Ephemeral Shields

Convoke on a protection trick puts the payment mechanism and the payoff in tension, and the tension is the whole point. Indestructible is the cleanest version of protection white sells: it ignores toughness entirely, so it walls a creature against burn, lethal combat damage, targeted destruction, and the board-wide sweeper alike. To cast it for a discount you tap untapped creatures, and that is exactly the bind: the bodies you tap to pay are bodies that can no longer block or attack this turn, and an attacker without vigilance is already tapped and cannot help pay at all. So the spell asks a player with a wide, untapped board to spend that width keeping one threat alive, which means it works best before combat or held back as an end-of-turn answer rather than mid-swing. What it does not do is just as defining: indestructible is blind to bounce, exile, and minus-toughness effects, so the protection it offers is total in one direction and useless in another. Edicts walk past it too, since the creature survives but the sacrifice still happens. As a common-rarity combat-and-removal answer it is honest white, rewarding the kind of go-wide board that can afford to convert tapped creatures into a saved one. The reason it reads as more than a generic save-your-guy instant is that the discount and the protection both demand the same resource: a board you were already planning to commit.