They're saying you should be compensated and make income for the time it took you to form the business and hire employees. You shouldn't (in their theory) then continue to earn income off the labor of the people you hired - the income they generate from their labor belongs to the laborer. You can also continue to make a salary from the business in exchange for the direct labor you do - management, accounting, whatever else. But if you stop working for 5 years and retire to a beach, you shouldn't be extracting continued income from the workers while you do nothing.

Investing as people think about it only exists because people who invest expect value from the thing they invest in. That value only exists because of a mixture of current and future expected income from the business. If the business itself doesn't generate income for people who aren't doing the actual labor, there's no reason to invest unless you have a personal interest in the continuation of the business, i.e. you're an employee whose income depends on that job. In this scenario you'd have employee-owned businesses.

Obviously this raises the question of where funding comes for new innovation and growth (public investment banks, worker cooperative financing, government grants), but then it goes down a rabbit hole about alternatives to capitalism.