Children become adult apostles to proclaim the Word. Large populations raise the standard of living by providing a wide variety of goods and services. Also, these services are provided at a lower cost per person. For example, a small town with a population of 1000 people cannot afford its own water sanitation plant. At least 100,000 people are needed.
Large populations are necessary to support a telephone industry or an automobile industry.
The United States is the third most populous nation on earth, after China and India. Population and a free market made it prosperous. It is not for us to know. The earth has 6 billion people. It can hold 600 billion or more.