You can think of the energy of the reactants and products as valleys separated by a mountain. The "normal" reaction requires the reactants in their base energy

You can think of the energy of the reactants and products as valleys separated by a mountain. The "normal" reaction requires the reactants in their base energy state (the bottom of the valley) to climb up the whole mountain, thus it will be very slow. The "just add enough heat" method is like flooding the whole mountain range up to the peak -- it technically works but causes other issues. Adding a catalyst is like digging a tunnel through the mountain.