The Book of Mormon was written to all the ends of the earth (see Mormon 3:18). However, these verses do not seem to be addressed to the non-Christian nations, but to the agnostics. They have had an opportunity to believe in Christ and have rejected him. The day of his visitation is his Second Coming, and his coming will be in power and glory causing the elements to melt in fervent heat. The question, “then will ye say there is no God,” implies they had said so before (v. 2). The same is implied in “Then will ye longer deny the Christ? Those who cannot behold the Lamb of God, the wicked, will be burned in the fire of his coming (see 3 Nephi 25:1; Malachi 4:1). The wicked will know, as most of them do now, that they are living contrary to the laws of God. Moroni’s point is an important one; they would be very unhappy living as an impure being with a pure and holy Being (Mormon 9:3–4). President Harold B. Lee has said: “You cannot have a Christlike life … without being born again. One could never be happy in the presence of the Holy One of Israel without this cleansing and purifying” (quotes Moroni 9:4). The purpose of life is to prepare us for the type of world, or the degree of righteousness we can endure.
34 And again, verily I say unto you, that which is governed by law is also preserved by law and perfected and sanctified by the same.
35 That which breaketh a law, and abideth not by law, but seeketh to become a law unto itself, and willeth to abide in sin, and altogether abideth in sin, cannot be sanctified by law, neither by mercy, justice, nor judgment. Therefore, they must remain filthy still. [D&C 84:34–35]
Those who are sanctified by law are those who live that law. Those who are sanctified by mercy are those who live the requirements of the Atonement to pay for their sins. Those who are sanctified by justice are those who suffer for their own sins, and following that payment are able to endure the glory for which they have prepared themselves (see 3 Nephi 12:26; Matthew 5:26; D&C 19:16–18). Thus, as Alma explained, This life is “a probationary state; a time to prepare to meet God; a time to prepare for that endless state … Which is after the resurrection of the dead” (Alma 12:24). At the time of our judgment at the bar of Christ, we will know where we belong, and will experience either an unquenchable fire, or be found spotless and pure through the Atonement (Mormon 9:5–6; see also 2 Nephi 9:15–18).