Does one have to believe Jesus is the Messiah of Israel to be saved?

John 20:30-31 NKJV

And truly Jesus did many other signs in the presence of His disciples, which are not written in this book; but these are written that you may believe that Jesus is the Christ, the Son of God, and that believing you may have life in His name.

Case closed

Some say all you have to do is believe in Jesus, not so