In this work, we integrate our previous success and progress into a unified microscopic mechanism that explains all of the experimentally observed VSC effects, giving the resonance condition , the normal incidence condition , the collective effect , and operating under the thermally activated condition. We consider a theoretical model where cavity mode couples to a set of solvent vibrations {Q j } (spectator modes, or rate promoting vibrations) which in turn couple to a reaction coordinate R 0 . This is a model that captures the essential feature of the recent VSC experiments , as well as classical simulations that demonstrate the collective effect for reaction rate constant or vibrational energy relaxation . We use the effective spectral density theory to treat how cavity mode collectively coupled to the spectator modes can influence the forward reaction along a given reaction coordinate R 0 , and derive an analytic rate constant expression based on Fermi's Golden Rule (FGR). We further use numerically exact quantum dynamics simulation based on the Hierarchical Equations of Motion (HEOM) approach to verify the accuracy of the theory. We discuss the fundamental mechanism of VSCsuppressed reaction, the basic scaling of VSC effects with light-matter coupling strengths, the null effect, and collective as well as normal incidence conditions.