The angel instructed Benjamin that those who sinned in ignorance would be saved by the atonement. He now prophesies of a day when very few will fall into that category, for the knowledge of the Savior shall spread until the inhabitants of the earth are left without excuse. One could argue that he is speaking of our day, when the world knows of Jesus Christ yet chooses to ignore his holy sacrifice. And so the missionary work continues until the day when the world has been sufficiently warned, this Gospel of the Kingdom shall be preached in all the world, for a witness unto all nations, and then shall the end come, or the destruction of the wicked (JS Matt 1:31).