Social Contract
The idea that we all contribute so we can all benefit. Both the government and people can expect to receive something from the other, but also commit to carrying out their responsibilities as part of society.
Example:
The government ensures our health system has the resources necessary to meet our needs, and we pay the taxes necessary to provide the resources. The tax we pay is often less than the cost if we all purchased the service individually.
Visual idea: A handshake between people and government.