Muhammad bin Ishaq reported that Ibn `Abbas said that Rafi` bin Huraymilah said to the Messenger of Allah ﷺ , "O Muhammad! If you were truly a Messenger from Allah, as you claim, then ask Allah to speak to us directly, so that we hear His Speech." So Allah revealed,

وَقَالَ الَّذِينَ لاَ يَعْلَمُونَ لَوْلاَ يُكَلِّمُنَا اللَّهُ أَوْ تَأْتِينَآ ءَايَةٌ

(And those who have no knowledge say: "Why does not Allah speak to us (face to face) or why does not a sign come to us")

The Jews, the Christians and the mushrikin used to deny the prophethood of Sayyidna Muhammad ﷺ and some of them did so out of sheer malevolence. In order to feel triumphant in this obstinacy, they would make absurd and impossible demands, two of which have been mentioned here. To begin with, they insisted that Allah Himself should speak to them, either directly as He speaks to the angels, or through the angels as He speaks to the prophets, and that He should Himself proclaim his injunctions to them so as to make the intervention of a new prophet unnecessary, or should at least announce that He had sent Sayyidna Muhammad ﷺ as a prophet, thus making it easy for them to have faith in him and to follow his guidance. Should Allah choose not to accept this demand, they were ready with another -- that is, Allah should send them a sign or proof in confirmation of his prophethood.

In reply to them, Allah puts this demand down as being no more than a foolish custom which has all along been unthinkingly practised by ignorant people even in the earlier ages. Then, the verse traces the origin of this demand to a distortion of the heart, in respect of which all the ignorant people, past or present, are alike, hence the parrot-like repetition of the same demand throughout the ages.