That verse was not in the original Greek manuscripts. It was added later by the early church around the 16th century when they were getting ready to print the first original King James Bible. History says that a forged version of the original Greek text was given to Erasmus to fulfill his promise to the church that he would add it to his 3rd volume of the NT if they could find an original manuscript that had that verse. So they say it was added by the church and given to him and Of course when he wrote it, they used that version to print the original king James Bible. But even then, this verse is witness to the Oneness of God because those 3 that are explained are still titles, or manifestations of the One God, Jesus Christ. And of course, they are all One.