John's former testimony was more private to the common people; this testimony was given to a public authority. The Jews (most probably the rulers of the Jews, who made up their sanhedrim, or great court, answering a parliament with us, for the cognizance of false prophets belonged to them) sent priests and Levites, which were Pharisees, 1 Thessalonians 1:24, of the strictest sect of the Jews as to rites and ceremonies; these came from Jerusalem, where the sanhedrim constantly sat, and the chief priests were, (if the message were not from the sanhedrim itself), to ask John Baptist who he was; that is, by what authority he preached and baptized? What kind of prophet he was? For they could not but know his name and family, he descending from a priest amongst them: and this appeareth to be their sense from what followeth.
Related Commentaries of John 1:19
John 1:19
19 And this is the record of John, when the Jews sent priests and Levites from Jerusalem to ask him, Who art thou?