Need help with bond pricing formulas

[Dillinger4]

After reading an article on advanced bond concepts I find myself a bit confused with a formula they are using. Any help would be greatly appreciated.

Fundamentally, however, the price of a bond is the sum of the present values of all expected coupon payments plus the present value of the par value at maturity. Calculating bond price is simple: all we are doing is discounting the known future cash flows. Remember, to calculate present value--which is based on the assumption that each payment is re-invested at some interest rate once it is received--we have to know the interest rate that would earn us a known future value. For bond pricing, this interest rate is the required yield.

Here is the formula for calculating a bond's price, which uses the basic present value (PV) formula:

Bond Price = C / (1 + i) + C / (1 + i)².. C / (1 + i)ⁿ + M / (1 + i)ⁿ

C = coupon payment
n = number of payments
i = interest rate, or required yield
M = value at maturity, or par value

Why would the interest rate have to be factored in? The coupon is the interested rate paid (typically semiannually).