Part 6 (AYAT-AL-KURSI)

The third sentence is "سِنَةٌ۬ وَلَا نَوۡمٌ۬‌ۚ", "Neither doze overtakes Him, nor sleep." The word سِنَةٌ۬ (sinatun)  drowsiness that starts before sleep, while the word نَوۡمٌ۬‌ۚ (nawm) refers to full sleep. The meaning of the sentence is that Allah Ta'alah is above and beyond state of drowsiness or sleep. When the word 'Qayyum' was used to inform that Allah Ta'alah is holding in perfect working order the whole universe, with everything in it, a human being could wonder whether a Being which is carrying out such a massive task all the time, gets tired or drowsy sometimes. In this sentence, man, who has limited knowledge, abilities, and insight, has been warned not to try to understand Allah Ta'alah on his own analogy, or that of other created beings. Allah Ta'alah is beyond such analogies. His power is absolutely perfect and these matters are neither difficult, nor tiresome, for Him. 

From Ma'ariful Quran, by Mufti Muhammad Shafi RE