There are two aspects to this. The first is that it is intended that the night and the day are signs in themselves. So, the addition in the verse of the night and the verse of the day is for clarification, like the addition of the number to the counted item. That is: We erased the sign that is the night and made the sign that is the day clear. The second is that it is intended: and We made the night and the day two signs, referring to the sun and the moon. We erased the sign of the night: that is, We made the night devoid of light, obscured and dark, in which nothing can be distinguished, just as nothing can be distinguished in a erased tablet. And We made the day clear, meaning that things can be seen and distinguished in it. Or, We erased the sign of the night which is the moon, as it was not created with a radiance like the radiance of the sun, so that you can see things clearly. And We made the sun radiant, in whose light everything can be seen, so that you may seek bounty from your Lord, to enable you, by the brightness of the day, to distinguish your deeds and manage your livelihoods. And to know by the alternation of the two new ones the number of years and the nature of the account, and what you need from it. Were it not for that, no one would know the calculation of times, and matters would come to a standstill, and everything you depend on in your religion and your worldly affairs would be disrupted. We have detailed it, clarified it in a clear manner, so We removed your excuses, and We left you no argument against us.