There again, I believe he is referring to that which will be poured out on the earth after the 7th seal. By the use of "His" wrath divides the tribulation and this division is centered around the "day of the Lord". The book of Revelation is not chronological - but you probably know this.
The wrath begins with the first seal in Chapter 6. There isn’t space enough here to go into but here is a site that begins to explain for those who are interested.
The first three chapters are dealing with the church age but chapter 4 begins with “hereafter”. It’s after the church aged because the “fullness of the Gentiles” has come and the church was taken from the earth. It’s after that we see a shift and the attention is in heaven and what is going to happen to the earth and those on it.
http://www.jesusisthecomingking.com/2011/03/when-does-gods-wrath-start.html
>> The book of Revelation is not chronological -<<
I disagree with that statement. Again, because of space I will simply list one site that helps explain.
http://prophecy.landmarkbiblebaptist.net/rev-chronology.html