Most biological reactions proceed at very slow rates under normal conditions. These rates are too slow for cells to grow and maintain normal cellular functions. The rates of these reactions can be increased by raising the temperature of the environment or lowering the activation energy of the reaction.
Most biological systems have a low tolerance for high temperatures.
In addition, temperature regulation requires a high input of energy into a system. Therefore, biological systems have evolved enzymes. Enzymes are biological catalysts. Their function is to lower the activation energy of specific chemical reactions, thereby allowing the reactions to proceed at rates faster than under standard conditions. Without their presence in the cell, the multitude of chemical reactions that make life possible would not proceed at the required rate.