Covenant of Blood

The printed seven-mana sticker is a fiction the keyword is built to expose. Read it as written and this looks unplayable in any deck that pays for spells with lands: four damage and four life is a fine package, but nobody is leaving six generic and a black floating to buy it. Convoke rewrites the math against board state. Every creature you tap shaves a generic off the bill, so a wide position fires this for a single black or close to nothing, spending the surplus bodies an aggressive board already has lying around between attacks. That is the trade convoke always negotiates: nominal cost against development. Hold it with an empty battlefield and it is dead weight; cast it off a developed army and the price collapses. The effect itself is the all-purpose payoff convoke exists to subsidize, with no target restriction: four to a face or a blocker, four life back, and the lifegain matters because a go-wide army is usually racing and paying down its own clock. Being a sorcery sets the window precisely. This is precombat or postcombat, never a combat trick, which means the creatures funding it are creatures that sat out the swing (or that you tapped before declaring attackers). It functions as a closer dressed as a haymaker: a way for a token or weenie strategy to push the last points through while clawing back the life it spent getting there.