Another explanation of the verse, ‘[The Torah] is more precious than pearls, and all your possessions cannot compare to it’, is that pearls are valued by weight. The heavier they are, the more they cost. But the ratio is exponential, and a pearl that weighs double the weight of another pearl will not be worth double, but rather many times more. The reason for this is that the heavier it is, the rarer it is.
So it is also with Torah, the more a person learns, the more valuable every minute of his time becomes. The more he learns, the more precious his learning becomes, the higher each new learning brings him, and the more refined his neshama becomes, ad infinitum.