What is the origin of the idiom "at one's beck and call" and when to use it?

The idiom "at one's beck and call" originated in the past when social roles and hierarchies were more pronounced. It means that someone is always ready and willing to respond to the requests or commands of another person. It implies a strong level of obedience and availability, indicating that the person being referred to is constantly at the service and disposal of someone else. It is often used to depict relationships with power dynamics, such as employer-employee relationships or situations involving personal assistants or service staff.