In order to increase their profits, people allocate more resources to achieve those goals. but when the means are scarce, it is only possible to satisfy the immediate needs; even, barely. Such shortage does not allow him to create new means to produce more; situation that is reversed once your earnings increase and you can devote more resources to invest in improving their conditions.
Every individual works for something. Nobody is going to dedicate their effort if there is not a result that benefits them. this indicates that for the human being to survive, wealth must be expanded. Therefore, the expansion of wealth implies positive return and that leads to the generation of wealth, since this way it is possible to satisfy basic human needs and sustain the situation in the context, which then makes savings possible, which It allows investment, which allows creating new sources to create even greater wealth.
The savings allow the expansion of wealth. And having these resources that can be assigned to achieve higher goals and longer time periods, create a preference for future goods, which causes interest rates to decrease.