John 17:3

John 17:3. And this is life eternal, that they might know thee the only true God, and Jesus Christ, whom thou hast sent.

This does not mean mere head-knowledge; but to know in the heart and soul the one only true God, and Jesus Christ who was sent of him to the sons of men, "this is life eternal." God without Christ brings not eternal life, and Christ, if he were not sent of God, would not bring eternal life to us, but knowing God in Christ Jesus is eternal life.