Note that this verse does not tell us to believe on the Father, Son and Holy Spirit. It tells us to believe on the Lord Jesus Christ who is: → the Father → the Son → the Holy Spirit
This is what Chrisitanity is all about - recognizing God in Christ Jesus so that we no longer flounder around in speculation and confusion. → Jesus is the Way to God. → Jesus is the Truth about God. → Jesus is the Life of God. → Jesus is God.