Not every reaction is spontaneous. Some reactions are very slow and some are very fast. It is the catalyst that speeds up the rate of reaction by decreasing the activation energy required by the reaction to proceed.
Chemical reactions are also integral part of living organisms. Every process in the living cell is chemically coordinated. Here role of catalyst is performed by the enzymes. Enzymes are the special proteins that speed up many biological reactions that are else would take several days or even weeks in their absence. Enzymes are more efficient than chemical catalysts. Chemical catalyst and enzymes are recovered in an unaltered form at the end of the reaction.