In his book ?The Plan of the Ages? Russell wrote that the preaching obligation of Matt.24:14 was already fulfilled by his time (italics original):
There are two texts chiefly relied upon by those who claim that the Lord will not come until after the Millenium, to which we would here call attention. One is, ?This gospel of yhe kingdom shall be preached in all the world for a witness unto all nations; and then shall end come.? (Matt. 24:14) They claim this as having reference to the conversion of the world before the end of the Gospel age. But witnessing to the world does not imply the conversion of the world. The text says nothing about how the testimony will be received. This witness has already been given. In 1861 the reports of the Bible Societies shoved that the Gospel had been published in every language of earth, though not all of earth?s millions had received it. No, not one half of the sixteen hundred millions living have ever heard the name of Jesus. Yet the condition of the text is fulfilled: the gospel has been preached in all the world for a witness ? to every nation. (The Plan of the Ages, 1908 and 1916 editions pp. 91-92)