‘And this is the witness of John when the Judaisers sent priests and Levites to him from Jerusalem to ask him, “Who are you?”
There were many ideas around at this time as to whom God would send to help His people. Some expected the return in bodily form of Elijah the Prophet himself (Malachi 4:5), remembering that he had never died but had been taken up by God alive (2 Kings 1:11), others expected a uniquely great prophet ‘like Moses' (Deuteronomy 18:15), others expected a Messiah (in Greek ‘Christos' - ‘anointed one') - or even more than one Messiah - who would, by God's power, deliver Israel, a deliverance usually thought of as happening by raising up an army from among the Jews. Thus they wanted to know exactly what John's claim was.
‘The Judaisers.' In this case the Pharisees (John 1:24). They sent Priests and Levites of their number because these would be seen as having special authority, for the priests were officially guardians and teachers of the truth. The Levites were Temple servants. The Pharisees would have had a special interest in his act of baptising (drenching) in water those who responded to his teaching, for they too practised many kinds of washings. But nothing of an initiatory flavour like John's (unless we count the bathing required of proselytes. That, however, was self-administered and intended to remove the uncleanness of the Gentile world to which they had belonged).