Basically, in order for a reaction to take place, the reactant molecules need enough energy in order to successfully collide with another to form the products. This energy is known as the activation energy.
What a catalyst does is provide an alternate path (one with a lower activation energy) for the molecules to successfully collide. This means that more molecules now can react as the energy requirement for this path is much lower, thus increasing the interactions and thus the rate of the reaction.
Perhaps you meant equilibrium position. "Equilibrium positive" is a term that I've never heard of.
Consider the reaction: with equilibrium constant: .
Equilibrium position refers to the amount of reactants and products that are in the mixture. Remember, the equilibrium constant remains the same (given we're working at the same temperature) and thus, the ratio between the products and reactants must stay the same.
Now I'm not entirely sure what you mean by a system resisting change. Any chemical reaction is subject to change in its equilibrium position by Le Chatelier's principle. Perhaps you're talking about buffers? I doubt that this is the case given the topic you're currently studying ...