'You are nothing but a human like us.' This means: What is the reason for your distinction over us with the message? And can a messenger be from among humans? Their following of the description without any conjunction indicates that they are not certain in their denial of him. The two descriptions to them are of the same status, just as if it were said: 'The pomegranate is sweet and sour,' meaning: it is a mixture. The fact that they remain in a state of doubt and have not moved beyond it to certainty or suspicion of denial is supported by their saying: 'So bring us a sign.' This means: a sign that indicates to us your truthfulness, 'if you are' meaning: a state that is in the utmost firmness, 'of the truthful' meaning: those who are deeply rooted in truthfulness, unlike what will come soon in the story of Shu'ayb, blessings and peace be upon him.