The church believed in recent years that the ministry of Herbert Armstrong fulfilled this verse, but subsequent events force us to modify our understanding.
It is certain that the end did not come immediately upon the death of Herbert Armstrong. On the other hand, he indeed preached the gospel of the Kingdom of God around the world as it had not been proclaimed since the first century. Though he technically did not witness before every nation, the preaching and literature of the church of God blanketed the globe in a way never done before.
In the context of Matthew 24, however, the timing of this great work of preaching the gospel is wrong if it applies strictly to the ministry of Herbert Armstrong. In the paragraph running between verses 4 and 14, this statement appears at the end of the context, after the opening of the fifth seal (verse 9; see Revelation 6:9-11). Thus, verse 14 seems to indicate a ministry active during the Great Tribulation, the subject Jesus expands on in verses 15-28.
What ministry is active on a worldwide scale during the Great Tribulation? None other than the Two Witnesses! From the summary of that ministry in Revelation 11, we can easily see that God empowers them during the 3½ years of the Tribulation (verse 3). Their ministry is called a "testimony" (verse 7), the same Greek word translated as "witness" in Matthew 24:14. When the Beast finally kills them in Jerusalem, everyone on earth rejoices (Revelation 11:10), indicating that the witnesses' work is worldwide. And three and a half days after their deaths, Christ returns and the age ends (verses 11-13; Zechariah 14:3-5).
Mr. Armstrong would probably be the first to admit this. When he told the church near the end of his life that the preaching of the gospel had been done, he could not have been ignorant of the work of the Two Witnesses. It is clear he meant that he had finished the work God raised him to do. That work revived the truth of God in many areas and prepared the way for the ministry of the Two Witnesses. However, we should see his ministry only as a type or precursor to the even greater work that will be done during the Great Tribulation.
Matthew 24:14 is indeed a definite sign of the end. It applies specifically to the very last days before Christ's second coming when God will give the world a final warning through the mouth of two witnesses (see II Corinthians 13:1; Deuteronomy 17:6).
Richard T. Ritenbaugh
Are These the Last Days? (Part 1)