Jacob supplements his scriptural testimony with his personal testimony. Jacob places his authority in both the scriptures and in the ultimate source of the scriptures, in Yahweh himself. Jacob has now placed pressure on Sherem from two directions—expounding the Messianic content of the scriptures and also asserting his own prophetic witness.
As a foreigner, Sherem did not know Jacob personally; and while it was his mission to discredit Jacob, his secular assumptions would have anticipated a sage but not a prophet.