Is the Trinity a Catholic invention?
No, it is not. You have heard the slander of the Jehovah’s Witnesses and other Unitarians that chose long ago to reject the Bible for their own opinions. All those who deny a plurality in the Godhead are condemned before they can finish the first chapter of Genesis, for the one God is a plural of divine Persons (Gen 1:26). At the other end of the Bible is John’s glorious testimony of three divine Persons being one God (I John 5:7). If you hear that I John 5:7 does not belong in the Bible, you are listening to an enemy and need the links below.
For a thorough defense of the authenticity of I John 5:7 … http://www.jesus-is-savior.com/Bible/1john57-exegesis.htm.