Final answer:
The evil spirit will bring seven more spirits when it comes back, which is a biblical reference representing the worsening of a person's state if they return to sinful ways.
Step-by-step explanation:
The number of spirits that the evil spirit will bring when he comes back is seven. This is a reference to a passage in the Bible, specifically from the Gospel of Matthew (12:45) and the Gospel of Luke (11:26), which describes an unclean spirit that, after being cast out, returns with seven other spirits more wicked than itself to re-enter the person.
This is a metaphorical teaching to convey the idea of a person being in a worse state if they fall back into their sinful ways after having been 'cleansed'.