What service did the beggars provide?

This is very simple!

In Buddhism, monks and nuns traditionally live by begging for alms, as did the historical Gautama Buddha himself. This is, among other reasons, so that lay people can gain religious merit by giving food, medicines, and other essential items to the monks. The monks seldom need to plead for food; in villages and towns throughout modern Thailand, Cambodia, Vietnam, and other Buddhist countries, householders can often be found at dawn every morning streaming down the road to the local temple to give food to the monks. In East Asia, monks and nuns were expected to farm or work for returns to feed themselves.