“Whoever confesses that Jesus is the Son of God, God abides in him, and he in God.” 1 John 4:15
This doctrine continues to divide the world, both theistic and atheistic, to this very day for good reason.
John’s point isn’t that the sole indicator of one’s salvation is simply calling Jesus “the son of God” (just read Mark 5:7-9).
John’s point (contextually) is that a failure to confess Jesus’ sonship stands as a key indicator of the spirit leading an individual.
Confessing Jesus as the Son of God is a test of the tongue that reveals the heart’s teacher. EA
“Jesus heard that they had cast him out; and when He had found him, He said to him, “Do you believe in the Son of God?” He answered and said, “Who is He, Lord, that I may believe in Him?” And Jesus said to him, “You have both seen Him and it is He who is talking with you.” Then he said, “Lord, I believe!” And he worshiped Him.” (John 9:35-38)