Revelation 6:12-17 shows that the Sixth
Seal represents the coming of Jesus and
the beginning of the Great and Terrible
Day of the Lord (vs 17).

It is the Day of Wrath spoken of so many
times in the Old Testament prophecies,
such as Zephaniah 1: 14-18:

" The great day of the LORD is near, it is
near, and hasteth greatly, even the voice
of the day of the LORD: the mighty man
shall cry there bitterly.
That day is a day of wrath, a day of
trouble and distress, a day of wasteness
and desolation, a day of darkness and
gloominess, a day of clouds and thick
darkness,
A day of the trumpet and alarm against
the fenced cities, and against the high
towers.
And I will bring distress upon men,
that they shall walk like blind men,
because they have sinned against the
LORD: and their blood shall be poured
out as dust, and their flesh as the dung.
Neither their silver nor their gold shall
be able to deliver them in the day of the
LORD's wrath; but the whole land shall
be devoured by the fire of his jealousy:
for he shall make even a speedy
riddance of all them that dwell in the
land."