Jesus has been with this congregation of Saints for a long time and he realized that he must leave. However, he knows they are still disturbed with numerous questions and so he tells them what to do until he returns the following day.
The element of urgency is pressing upon Jesus because he is scheduled to report back to the Father and then minister to the lost tribes. Of course the Nephites have no idea where the lost tribes were located and so Jesus assures them that the Father knows where he has taken them.
We have some interesting comments concerning the lost tribes in the Apocrypha by Esdras. The pertinent text from Esdress is quoted is Mormon Doctrine by Bruce McConkie under the topic of the lost tribes. Esdras indicates that when the ten tribes went northward, a portion of them, which we presume to be the more righteous, went even further north and disappeared. The remainder were left behind.
Brigham Young indicated that the more righteous group were taken to a separate planet. This reference can be found in Cowley's biography of Brigham Young on page 448. Soon after the gospel was restored, Joseph Smith learned that John the Revelator was with the lost tribes preparing them for their return. This is what the tenth Article of Faith is referring to when it says "We believe in the restoration of the Ten tribes."
Moses says that when this happens the lost tribes of Israel will be gathered from the "utmost parts of heaven."1 With this same thought in mind, Jesus says they will be gathered from one end of heaven to the other in Matthew 24:31. But that will not happen until after the building of the temple in the New Jerusalem.
In fact, Esdras says that when the lost tribes return they will be astonished to find that the house of Joseph whom they left behind will be in charge of the Lord's work throughout the world. Commenting on the first appearance of the lost tribes in the north lands a modern scripture says, "And they who are in the north countries shall come in remembrance before the Lord ... and they shall smite the rocks and ice shall flow down at their presence. And an highway shall be cast up in the midst of the great deep."2
This highway will lead directly to the temple in the New Jerusalem where the scripture says: "And there shall they fall down and be crowned with glory, even in Zion, by the hands of the servants of the Lord, even the children of Ephraim."3 Jeremiah says the raising up of this mighty highway with hundreds of thousands of the Israelites pouring over it will make the crossing of the Red Sea almost insignificant by comparison.4 The advantage of having these references in the commentary [which are located in the footnotes above] is so that you can always go back to each citation when it is convenient and read them for yourself.