John tells us the purpose of his book:
" 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."
"But those things which God foretold by the mouth of all His prophets, that the Christ would suffer, He has thus fulfilled. Repent [Ye men of Israel, brethren, etc.] therefore and be converted, that your sins may be blotted out, so that times of refreshing may come from the presence of the Lord, and that He may send Jesus Christ..." -Acts 3
"Most assuredly, I say to you, he who hears My word and believes in Him who sent Me HAS everlasting life, and SHALL NOT come into judgment, but HAS passed from death into life." -John 5:24