Evaluate an outstanding forward contract with a locked-in delivery price of K.
Buy one unit of the underlying asset at the spot price St and hold to time T.
Buy a forward contract to buy one unit of same underlying asset at the forward price K.
In order to have sufficient funds at maturity to pay K, we invest the present value of K in an interest-bearing account. This is the present value of Ke-rT.
We have to pay the market value of the outstanding long forward contract: Vt = St – Ke-rT