Surah 21. Al-Anbiya, Ayah 49

For an explanation of the above rendering of the expression bi’l-ghayb, see note [3] on 2:3 .

 This can also mean that they are in awe of their Lord as much in private as they are in public.

Note the three kinds of fear mentioned in xxi. 48-49. Taqwa is the fear of running counter to the will of Allah; it is akin to the love of Him; for we fear to offend those we love; it results in right conduct, and those who entertain it are "those who would do right". Then there is Khayat, the fear of Allah, lest the person who entertains it may be found, in his inmost thoughts, to be short of the standard which Allah wishes for him; this is also righteous but in a less high degree than Taqwa which is akin to love. And thirdly, there is the fear of consequences on the Day of Judgment (ishfaq); this also may lead to righteousness, but is on a still lower plane. Perhaps the three correspond to the Criterion, the Light, and the Message (or Warning) of the last verse.