Silk Net

Granting reach is the function here, and it dictates exactly when this card earns its mana. The +1/+1 is filler attached to a green answer for flying creatures, the color that historically had the worst tools against them. Where blue had counters and white had its own evasion to trade up, green's plan against an attacker in the air was to race it on the ground and hope the math came out ahead. This hands a blocker the keyword it needs to make the block legal at all, at instant speed, so the trick lands inside the combat step after attackers are declared. That timing is the design discipline: a permanent reach-granting effect would just be a worse creature, but pricing it as a one-shot combat instant means it ambushes a flyer the turn it commits to the red zone, spending one card to trade with an attacker the defender otherwise could not touch. The bear-fight math is unflattering on rate, which is why green eventually got cleaner answers that simply destroyed flying creatures outright. What this represents is an earlier era's solution to a structural color-pie problem: green could not remove a flyer, so it was given a way to reach up and meet one in combat instead.