The separate realms of earth and heaven have different qualities and different purposes. God reigns in heaven where his word is literally law. On this earth, however, agency reigns in all of its glorious promise and wonderful confusion. God’s word may be the rule of heaven, but on earth it (in the form of scripture) is no more binding than a parent’s counsel—and is obeyed about as often. Nevertheless, agency allows us to accept that word and implement it in our lives. Thus, we should pray that the heavenly will become part of our earthly experience. We pray to bring heaven into this earth and into our hearts.
Comparison: 3 Nephi removes the first phrase from the Matthean text:
Thy kingdom come.Thy will be done in earth, as it is in heaven. (Matt. 6:10)
This deletion is unusual. It is quite certain that it appeared in the Old World version of the prayer. It parallels Luke 11:2 and is corroborated in the Didaché, a second-century church manual:
You must not pray like the hypocrites, but “pray as follows” as the Lord bid us in his gospel:
Our Father in heaven, hallowed be thy name; your kingdom come; your will be done on earth as it is in heaven; give us today our bread for the morrow; and forgive us our debt as we forgive our debtors. And do not lead us into temptation, but save us from the evil one, for yours is the power and the glory for ever.
The phrase is a logical extension of God’s kingdom as equally present both on earth and in heaven. Do differences between the Old and New World contexts account for its removal? Could the phrase’s removal have to do with the Messianic implications of “thy kingdom come”? This is the position Robert J. Matthews supports: “The biblical account of the prayer includes the phrase ‘Thy kingdom come’ (Matt. 6:10). The Nephite sermon does not contain this phrase (3 Ne. 13:9–10), evidently because the kingdom of God had already come to the Nephites. The record itself makes this clear, since it shows that the Nephites had prophets among them who were baptizing, conferring the Holy Ghost, and doing many things that pertain to the kingdom.”
Nevertheless, this is not a very persuasive argument. The nature of the other changes made for the Book of Mormon translation from the Matthean text are most easily seen as coming from Joseph Smith rather than the underlying plate text. It would seem more parsimonious to use the same explanation for the absence of this phrase. Perhaps Joseph intentionally removed the phrase because the Nephite God had literally come. However, I see little indication that Joseph was aware of that aspect of Nephite theology. I suspect that the absence is most likely explained as an error.