It was time to leave the Nephites.  Jesus had other work to do.  Jesus wanted to give each of His 12 disciples a gift. He asked them one by one what they most desired.  9 asked that after they lived to the age of man they might come speedily back to live with Christ in Heaven.  The other 3 wanted to stay just like John the Beloved did, until Jesus comes again for His 2nd coming.  They wanted to continue doing the same missionary work they were doing, teaching and baptizing and working miracles.  Jesus changed their bodies, so they were sanctified and Satan can have no hold on them.  They are on the earth now doing God’s work until He comes again.