This tells us about the specificity of enzymes.
Since in the lock and key model, the lock is only suitable for one key to unlock, only one pattern of key is able to do that, so, to compare it with enzymes, it means that the active site of enzyme is only suitable to bind one type of substrate to it, not other substrates.
We call this property of enzyme the specificity of enzyme. If the active site of an enzyme is changed or loss its three dimensional patterns, it can no longer function as a biological catalysts to speed up chemical reactions.