On several occasions, the day of the Lord is referred to as the “great day” (Joel 2:31; Zephaniah 1:14). That the day is called “great” indicates that it is an extraordinary day, unlike other days (Jeremiah 30:7). The word translated “awesome” has at root the connotation of fear. The day is “awesome” insofar that it will cause great fear among the ungodly. For them it will be “dreadful” day. This same combination “great and awesome” is used to describe God himself (Deuteronomy 7:21; Daniel 9:4; Nehemiah 1:5; Nehemiah 4:8). Since God is himself “great and awesome, it is no wonder that the day of the Lord in which he acts will also be great and awesome.
5 “Behold, I will send you Elijah the prophet before the great and awesome day of the LORD comes.