What is meant by believing "in the like of that which you believe"?

Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. It means: "If they have belief like your belief". [Ibn al-Anbārī]
2. It refers to "the Scripture" (al-Kitāb). The interpretation is: "If they believe in your book as you believe in their book". [Abū Muʿādh al-Naḥwī]
3. The word "like" (mithl) here is negligible, and the meaning is: "If they believe in what you believe in".