One way to understand it is that the Gemara is comparing the first three things with the last. It is a natural and universally accepted belief that the more and harder one works to earn a living, the more successful he will be at earning money. If one sits back and does nothing, he will not earn money, and whatever funds he has will dissipate.

One should incorporate that natural drive into his spiritual pursuits as well. Only if one constantly works on his Torah learning, good deeds and prayer will he be successful and thrive in those areas. If one does not constantly work on those areas, then not only will he not grow, but his Torah knowledge, good deeds, and prayer will decline in quantity and quality.

M. Kornfeld