Surah 87. Al-Ala, Ayah 6

The soul, as it reaches the Light of Allah, makes gradual progress, like a man going from darkness into light. So the Qur-an was revealed by stages. So all revelation from Allah comes by stages. As usual, there are two parallel meanings: (1) that connected with the occasion of direct inspiration to the holy Prophet; and (2) the more general Message to mankind for all time. Everyone who understands the Message must declare it, in words, and still more, in his conduct.

The particular occasion was an assurance to the Prophet, that though he was unleftered, the Message given to him would be preserved in his heart and in the hearts of men. The more general sense is that mankind, having once seized great spiritual truths, will hold fast to them, except as qualified in the following verse.