The authorities summon the healed man again and say, 'Give God the praise: we know that this man is a sinner.' In this setting the phrase functions differently from a modern worship exhortation.
They are pressing the man to speak truthfully under the authority of God.
A close biblical parallel appears in Joshua 7:19, where Joshua tells Achan, 'give, I pray thee, glory to the LORD God of Israel, and make confession unto him; and tell me now what thou hast done.' The expression can therefore introduce a solemn demand for truthful admission or testimony.
Ironically, the interrogators immediately tell the healed man what conclusion they expect him to affirm about Jesus.
Recognizing the formula changes the tone of the scene. The authorities are not asking the man to interrupt the hearing for a moment of praise; they are effectively placing him under a religious obligation to tell the truth.
His answer is memorable because he refuses their prescribed conclusion and sticks to what he knows firsthand: 'whereas I was blind, now I see.'