The vibrational and rotational mode specificity of the Cl + H2O -> HCl + OH reaction is studied on a recently constructed ab initio based global potential energy surface using an initial state selected Chebyshev real wave packet method. The full-dimensional-quantum dynamical results under the centrifugal sudden and/or J-shifting approximations indicate that this reaction is enhanced strongly by excitations of the stretching modes of the H2O reactant but only weakly by bending excitations. On the other hand, combination modes are found to enhance the reaction more than the sum of individual excitations. In addition, rotational excitation of the H2O reactant slightly inhibits the reactivity. The observed mode specificity is consistent with the predictions of the recently proposed Sudden Vector Projection model, which attributes the promotional effects of the reactant modes to their couplings with the reaction coordinate at the transition state.