If the devil believed in Jesus He would not have rebelled. You are very confused.
What did the devil not believe about Jesus?
We are not told but i'm sure the devil Knew that Jesus was almight and was righteous, and just, and all the fruits the devil seen.
Today people can believe that Jesus is the Lord and believe that Jesus is the messiah but love sin more then Jesus.
As a result of loving sin more then Jesus they never commit to follow or surrender their lives to Him.
Baptism is a choice to be born again.
Mat 10:37 He that loveth father or mother more than me is not worthy of me: and he that loveth son or daughter more than me is not worthy of me.
Mat 10:38 And he that taketh not his cross, and followeth after me, is not worthy of me.
Mat 10:39 He that findeth his life shall lose it: and he that loseth his life for my sake shall find it.
Many people believe in Jesus and know that He is the way of salvation but want sin more then they want Jesus.
Believing is not enough..
Faith without works is dead.