Question

Governments must provide some goods and services because

Answer 1

If the government doesn't provide some goods and services there cannot be a stable economy. Supply and demand wouldn't be able to be met. 

Answer 2

Governments must provide some goods and services because public goods are non-rivalrous and non-excludable and are not subject to the exclusion principle. This means that every person has the right to enjoy these products. Public services are not provided by the free market.
In contrast to this, private goods are rivalrous, which means that only people who are willing and able to pay can enjoy the product.