Standing on the Point of a Needle (MK36c)

KOAN:

Why is it that someone who can dive into the sea and count the grains of sand is standing on tiptoe on the point of a needle?

—PZI Miscellaneous Koans, Case 36c

From Xutang Zhiyu’s Three Barriers:

a. How can an unenlightened person put on clothes made of emptiness?
b. If an enlightened person draws up the plan for a prison on the ground, why can’t they get out?
c. Why is it that someone who can dive into the sea and count the grains of sand is standing on tiptoe (or sitting?) on the point of a needle?