What is the origin of the idiom "Sunday best" and when to use it?

The origin of the idiom can be traced back to the practice of wearing one's best or finest clothing on Sundays, traditionally considered a day of religious observance and rest. It is used to refer to one's finest or most formal clothing, typically reserved for special occasions or events. The phrase conveys a sense of dressing up or making an extra effort to look one's best for a particular event, such as a wedding, a job interview, or any situation where a more formal or distinguished appearance is desired. It is often associated with wearing formal or dressy clothing rather than casual or everyday attire.