humphry davy determined the nature of chemical bonds.
a catalyst doesn't change the relative energies of reactants and products
a catalyst speeds up a reaction by providing an alternate pathway with a lower activation energy (see image).
more molecules will have enough energy to get over the energy barrier, and the product is formed faster.
a catalyst does not change the energies of the reactants, so it does not change the amount of product at equilibrium.
thus, if the end of the reaction (equilibrium) is reached quickly, a catalyst does not affect the amount of product.
if an uncatalyzed reaction takes a long time (say, a hundred years), then the addition of a catalyst will cause more product to be formed during a laboratory period, but it won't affect the amount formed at equilibrium.