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 Ft.
In order to have sufficient funds at maturity to pay Ft, we invest the present value of Ft in an interest-bearing account.
This is the present value of Fte-rT
Assume the interest rates are continuously compounded, so the present value of a dollar paid at expiration is PV($1) = e-rT
The initial cost of forward value is zero Vt = St – F = 0 St – Fte-rT = 0 St = Fte-rT Ft = SterT