God's actual given word is the standard.
Remember what Jesus told the unbelievers, John 8:47, He that is of God heareth God's words: ye therefore hear them not, because ye are not of God.
The Apostle John explained in 1 John 5:9-13, . . . He that believeth on the Son of God hath the witness in himself: . . .
And in 1 John 2:27, But the anointing which ye have received of him abideth in you, and ye need not that any man teach you: but as the same anointing teacheth you of all things, and is truth, and is no lie, and even as it hath taught you, ye shall abide in him.