I've referred to these verses before. When Elder Mark E. Peterson claimed the Lord would not visit with "gentiles" but only with the house of Israel relying upon 3 Nephi 15: 23, it was my view that the 3rd Nephi statement of Christ was as to His immediate post-resurrection appearances to the various scattered lost tribes. He had no commission from the Father to appear to the gentiles in that time frame. These verses are about a different, much later time. These are speaking of the time when the Book of Mormon (record of the Nephties) would come into the possession of the gentiles. The gentiles will, if they hearken to the "Lamb of God IN THAT DAY," have the Lamb manifest Himself to them. Today is THAT DAY. It is now when the gentiles are promised He will manifest Himself to us, in "word" and in "power" and "in very deed."
His assignment immediately post-resurrection was to visit with each of the still organized, prophet-led, but scattered children of Israel. They had been put into the "nethermost" parts of the earth. He went to and visited with each of them serially. He did not visit with gentiles during that ministry.
But in the time following the publication of the Book of Mormon, and as part of removing the stumbling blocks of the gentiles, He is to visit the gentiles "in word" and "in power" and "in deed" so that it will "take away their stumbling blocks."
What does it mean to stumble? What is a "stumbling block?" What kinds of things would impede you from walking back to the presence of God? How will Christ's ministry in "word, power and deed" to gentiles remove these things?
It is AFTER the ministry of "word, power and deed" when the stumbling blocks are removed, that the gentiles are then "numbered among the seed of thy father." Note that they are not numbered among other branches of Israel. Note that they are not sealed to their fathers and made Ephriamites descended from other branches. They are to be "numbered among the seed of thy father" or counted as part of Lehi's seed. They are, in short, to be sealed to Lehi as their Patriarch and father. It is necessary to understand the doctrine discussed in this post.
This was always a part of the Gospel. Joseph Smith understood it and practiced it. Today we think it was an oddity that got corrected at the time of Wilford Woodruff. However, if you read the Book of Abraham you realize that the adoption of people into an inheritance was always the manner the Celestial Kingdom was to be organized here. Look at the Lord's discussion/explanation to Abraham found in Abraham 2: 8-11:
Those who receive the same priesthood (Patriarchal) from the time of Abraham forward become his (Abraham's) seed. Therefore they become his (Abraham's) inheritance and posterity, sealed to him as a part of his family.
This was the priesthood that was bestowed upon Joseph Smith, as a result of which he received the promises of Abraham. While looking for references to Abraham throughout Section 132 is interesting, I'll just take an excerpt. [PLEASE forget about plural wives while you read this. Think only about Patriarchal Priesthood and the authority which was with Abraham and renewed in Joseph. It is that issue that I want to focus, and not to become side-tracked on plural marriage. At some point I'll spend a few weeks on that side issue. NOT NOW.] So here is Section 132: 28-32:
Exaltation came through this priesthood, which linked together the fathers and the children of promise.The priestly sealing together of Patriarchs into a family that will endure as the government in heaven was the object of the Gospel in every generation. We are returning, at the end, to what it was at the beginning. However, the way in which it was to occur was "by my word" and "by revelation and commandment" so that the person knows he is to have a part in the Father's kingdom. It was not to be merely a distant expectation, uncertain in origin and doubtful in authority. It was to be certain, not doubtful: "The more sure word of prophecy means a man’s knowing that he is sealed up unto eternal life, by revelation and the spirit of prophecy, through the power of the Holy Priesthood." (D&C 131: 5.) It is directly connected with this Patriarchal Priesthood, the same authority which belonged to Abraham, the possession of which by any man makes him the seed of Abraham.
Returning to the subject of "remnant" and "gentiles," the Book of Mormon prophecies still do not refer to the latter-day gentiles as anything other than "gentiles" even when they are "numbered among the seed of Lehi." Gentiles retain in prophecy their identification with "gentiles" although they are adopted as Lehi's seed. Hence Joseph Smith's reference in the Kirtland Temple dedicatory prayer to the Latter-day Saints as "gentiles" by identity. (D&C 109: 60.) Whenever a gentile manages to acquire this adoption, they do not become identified as the "remnant" as a result. Instead, they become heirs to share in the promised blessings, but as "gentiles." They will get to assist the "remnant" but as "gentiles" not as the "remnant." Still, those who are adopted as Lehi's seed inherit with the "remnant" the Lord's promises. But they are nevertheless called in prophecy "gentiles" throughout.