What is the origin of the idiom "voice crying in the wilderness" and when to use it?

The idiom "voice crying in the wilderness" originates from the Bible, specifically from the Gospel of Matthew. It refers to John the Baptist, who was described as a voice proclaiming a message in the deserted wilderness, preparing the way for Jesus Christ. It is often used in discussions about activism, social change, or advocacy, highlighting the struggle of individuals who passionately advocate for their beliefs or ideas, even when they face resistance or indifference.