1 John 5:20
And we know that the Son of God is come, and hath given us an understanding, that we may know him that is true, and we are in him that is true, even in his Son Jesus Christ. This is the true God, and eternal life.
John testified to the fact that Jesus has come. The coming of Jesus has been revealed to us by the one who is true, God Himself, and through Him eternal life is found and can be experienced.