The Bible testifies about the Savior who will save mankind (John 5:39.) It means that we can recognize the Savior ONLY through the Bible.
You diligently study the Scriptures because you think that by them you possess eternal life. These are the Scriptures that testify about me [the Savior] (John 5:39)
We need to remember why God allowed us the Bible. Since we cannot see the spiritual world, God gave us the Bible for us to see the spiritual world and to receive the Savior who will lead us to the kingdom of heaven. God is almighty and does not need that any one should bear witness concerning man (John 2:25.) The ONLY criteria for recognizing the Christ is the Bible.
But how then would the Scriptures be fulfilled that say it must happen in this way? (Matthew 26:54)