The primary element of apocalyptic thought is what the Bible calls “the day of the Lord” (Isa. 13:6, 9; Ezek. 30:3; Joel 1:15; 2:1, 11, 31; 3:14; Amos 5:18; Obad. 15; Zeph. 1:7, 14; Zech. 14:1; Mal. 4:5; Acts 2:20; 1 Cor. 5:5; 1 Thess. 5:2; 2 Thess. 2:2; 2 Peter 3:10). Spoken of first in the early prophetic literature, the day of YHWH becomes the focal point of prophetic declaration since “similar terms, particularly ‘that day,’ ‘the day of,’ and ‘the day when,’ appear nearly 200 times in the prophets.” - John P. Harrigan, The Gospel of Christ Crucified, p.46