A scattering modeling approach is used to clarify the formation of the thermoreversible polymer gel with a fibrillar network We find that the gelation has to do with the spatiotemporal evolution of the so called 'coherent structure the nonlocalized fibril nucleation via the fluctuation instability and fibril growth coupled with a cooperatively coarsening concentration wave and is a direct consequence of the spinodal crystallization far from equilibrium in the solution The present result rejects the common opinion that the gelation is nothing more than the percolation problems and poses an interesting question about the entropy-driven crystallization