Textual: There are no changes from the Matthean version. However, the very fact that there are no changes raises issues for the nature of the translation. There is very weak textual support for this phrase in the earliest manuscripts, suggesting that it is a later addition to the Lord’s Prayer (Robert Guelich. A Foundation for Understanding the Sermon on the Mount. Word Publishing, Dallas. 1982, p. 297). For those who assume that Joseph Smith translated this material fresh from the plates, this provides an excuse to claim that he was no translator at all.
Of course this entirely misses the point. The translation method did not always require that Joseph translate anew from the plate text, and in particular it appears that it was preferable for the original modern audience that texts that resembled the KJV should also replicate the KJV. We are seeing not a condemnation of translation, but a definition of translation as Joseph used the term. Since he used the KJV Matthean text as the basis for the 3 Nephi Sermon, it is no surprise that this phrase should be retained.
Even if this phrasing is adopted later, it was probably adopted quite early, as we see a variant of it in Paul’s letter to the Corinthians:
1 Chronicles 29:11
11 Thine, O LORD, is the greatness, and the power, and the glory, and the victory, and the majesty: for all that is in the heaven and in the earth is thine; thine is the kingdom, O LORD, and thou art exalted as head above all.
It is quite probable that this combination of expressions was linked to a liturgical description of the Lord early in the Christian church, and therefore the early presence in Paul is part of that standard language, which is then added as the final phrasing to the Lord’s Prayer.