Why does an airliner use high thrust on the takeoff roll even though it will later land at a much slower speed?

Answer: Builds safe airspeed margin

Builds safe airspeed margin ✓ — Right. Near the runway the airplane is slow and has little room to trade altitude for speed, so thrust is mainly buying airspeed and climb margin quickly. Lift rises with velocity squared, so a small shortfall in speed is not a small shortfall in lift. Landing is different because flaps and slats reshape the wing for low-speed lift and extra drag.

Pushes air under the wings — Almost, but the engines are not simply inflating a pocket under the wing. Wings make lift from their shape, angle, area, air density, and speed through the air; the runway does not need to be packed with engine blast. This misconception feels natural because a jet blast is visible and loud, while the pressure pattern over the wing is invisible.

Reaches cruise speed early — No. Takeoff thrust is not trying to reach cruise speed before the airplane leaves the ground; cruise happens much later, high above the runway. The wing needs enough airspeed for liftoff and enough climb performance if something goes wrong soon after liftoff. The surprising part is that takeoff is not just 'start moving'; certification speeds are tied to controllability and climb requirements.