We will assume that both the forward and reverse reactions are elementary processes and that the value of the equilibrium constant is very large.
If both the forward and reverse reactions are elementary processes, then we can write the rate laws based upon the molecularity of the steps, right? So we have
Chemical equilibrium occurs when opposing reactions are occuring at equal rates; therefore, if our system is at equilibrium, then the rate of the forward reaction must equal the rate of the reverse reaction (this is just what we did when solving rate laws which contained intermediates):
thus, at equilibrium, the concentrations of products divided by the concentrations of reactants is a constant. If the equilibrium constant has a large value then the numerator of K must be larger than the denominator. If this is so, then the products must predominate.
If the equlibrium constant K is large then kf must be larger than kr, so the forward reaction has the larger kinetic rate constant.