For the great day of his wrath is come; and who shall be able to stand? 'The day, the great (day).' After the Lord has exhausted all His ordinary judgments-the sword, famine, pestilence, and wild beasts, and still sinners are impenitent-the last great day of the Lord itself shall come. Matthew 24:1-51 (note, Revelation 6:12, above) forms a perfect parallelism to the six seals, not only in the events, but the order: Revelation 6:3, the first seal; Revelation 6:6, the second; Revelation 6:7, the third; Revelation 6:8, end, the fourth; Revelation 6:9, the fifth; the persecutions, abounding iniquity, and consequent judgments, accompanied with Gospel-preaching to all nations as a "testimony," are detailed Revelation 6:9-17; Rev. 6:29 , the sixth.
To stand - justified, not condemned, before the Judge. Thus the sixth seal brings us close to the Lord's coming. The ungodly 'tribes of the earth' tremble at the signs of His immediate approach. Before He actually inflicts the blow, "the elect" must be 'gathered' out.