Consider the case of a microeconomy.
Let A = $500 / month
Let B = $100 / month
rate of spending in the economy = A + B
rate of building up capital (profit) = B
B = rate of building up capital in the balance sheets of firms
A = rate of return to various people (e.g. workers, leaders, investors, etc.) on spending performed by spenders (e.g. customers, individual buyers, other businesses, etc.)