Then said they unto him, Who art thou? that we may give an answer to them that sent us. What sayest thou of thyself?

They said then to him, 'Who art thou, that we may give an answer to those sending us? what dost thou say concerning thyself?'

So they pressed the question. "Who are you?" they said - "that we may take an answer to those who sent us. What account do you give of yourself?"

So they said to him, Who are you then? We have to give some answer to those who sent us. What have you to say about yourself?

"Who then are you?" they continued. "Tell us so that we have an answer to give to those who have sent us. What do you say about yourself?"

That we may give an answer to them that sent us - These Pharisees were probably a deputation from the grand Sanhedrin; the members of which, hearing of the success of the Baptist's preaching, were puzzled to know what to make of him, and seriously desired to hear from himself what he professed to be.

Then said they unto him, who art thou?.... Since, as yet, he had only answered in negatives, who he was not, that he was not the Christ, nor Elias, nor that prophet; they desire he would give them a positive account who he was:
that we may give answer to them that sent us; that their labour might not be in vain; that they might not come so far for nothing, without knowing who he was; and that they might be capable of giving an account of him to the sanhedrim:
what sayest thou of thyself? they insisted on it, that he would openly, and honestly declare who he was, and what was his office and business; that from his own mouth, and not from the opinion and conjectures of others, they might represent him in a true light to those who had deputed them on this errand.