Cnap 23 example 9 explanation

In chap 23 example 9 we calculate the future liability to its current present value using the discount rate so what is the point of calculating the PV of future liability ($21.840m) ?? Why do we calculate the PV of future liability because we have borrowed the money today but we have a liability in the future to be paid like a loan where we lets say borrowed $150,000 and we have to make monthly payment for the borrowed money so why are we calculating its current present value? Can you please explain?