What is the origin of the idiom "keep one's hand in" and when to use it?

The origin of the idiom "keep one's hand in" dates back to the 19th century, and it is believed to have originated from activities that require manual dexterity or skill, such as crafts or trades. It suggests the idea of maintaining proficiency or competence by occasionally practicing or engaging in a particular skill or activity, even if it is not one's primary focus. This idiomatic expression is used to convey the idea of staying proficient or skilled in a particular area of expertise, profession, or hobby by practicing or participating in it periodically, even if it's not the main focus of one's current activities. It implies that by doing so, a person can remain competent and ready to resume that activity more seriously if needed.