The great and terrible day of the Lord! The sky will be rolled up like a scroll, the blindness created by culture and sin will be shattered. I think of it as that moment when there is no hiding from the truth, either in head or in heart.
Like the way folk reacted to angels in the old testament, and God's descent to Mt Sinai? They were scared they would die! it's an emotional and heart-deep reaction, not a shallow one. A tiny glimpse of just what will happen when He comes to do justice!