What is the origin of the idiom "come rain or come shine" and when to use it?

The idiom "come rain or come shine" originated from the English language and is used to express unwavering commitment or dedication regardless of the circumstances or challenges faced. It is mainly used to convey the idea of remaining steadfast and resolute, whether it be in fulfilling a promise, completing a task, or maintaining loyalty. The phrase signifies a determination to persevere through both favorable and unfavorable conditions.