Why drag is important to skydivers?

Answer 1

A round parachute operates as an aerodynamic decelerator. The theory is to put out enough surface area that the resulting drag results in a fall rate that is survivable and that the jumper can walk away.

With rectangular parachutes, or ram air, the parachute is more akin to a glider. The parachute is a wing creating lift, so gravity powers it through the air, and drag keeps it from accelerating infinitely.