The following excerpt is taken from Tafsir Abdullah Yusuf Ali surah 21 verses 48-49:
48. In the past We granted to Moses and Aaron the Criterion (for judgment), and a Light and a Message for those who would do right —
C2709. Here three things are mentioned as given to Moses and Aaron:
1. The Criterion for judgment: this might well be the wonderful Proofs they saw of Allah’s goodness and glory from which they could have no doubt as to Allah’s will and command;
2. the Light; this was the inner enlightenment of their soul, such as comes from inspiration: and
49. Those who fear their Lord in their most secret thoughts,
and who hold the Hour (of Judgment) in awe.
– 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.
Yusuf Ali, Abdullah. Translation and Commentary of the Quran. (Surah 21 verses 48-49) http://www.quran4u.com/Tafsiraya/Index.htm