Translation
And who is the one who is victorious over the world, if not the one who believes that JESUS is the SON OF GOD?
Paraphrase
And who is the one who is victorious over the world, if not the one who believes that THE SAVIOR is GOD?
Context
John’s first epistle centers largely on the questions “Who is Jesus?” and “How can we identify a true follower of Jesus?” In the first 5 verses of chapter 5 Jesus is identified as the Christ (Messiah), and as the Son of God, which means God.