If you don't understand something, you can just Googled it.
To believe on
to accept implicitly as an object of religious trust or obedience; to have faith in.
https://www.thefreedictionary.com/To+believe+on
To believe in
To believe that the subject of the thought (if a person or thing) exists, or (if an event) that it has occurred, or will occur; - as, to
believe in the resurrection of the dead.
https://www.thefreedictionary.com/To+believe+in
The devils believe in Jesus - the subject exists, but they don't believe on - accept implicitly as an object of TRUST or OBEDIENCE.