31 But these are written that you may believea that Jesus is the Messiah, the Son of God, and that by believing you may have life in his name.

Read John 20:31 Using Other Translations

But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name.
but these are written so that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name.
But these are written so that you may continue to believe that Jesus is the Messiah, the Son of God, and that by believing in him you will have life by the power of his name.