This part of the story can be confusing. What happens here is that the Lord looks to the natural branches which have now grown into trees. He sees that they (scattered Israel) have become corrupted but recognizes the spiritual potential of these peoples. This response occurs because of the natural tendency of those of scattered Israel to believe:
“To the missionaries of the latter days the Lord has said: ’Ye are called to bring to pass the gathering of mine elect,’ for, the Lord explained, ‘mine elect hear my voice and harden not their hearts’ (D&C 29:7). For theirs was a ’believing blood.‘ ’What then is believing blood? It is the blood that flows in the veins of those who are the literal seed of Abraham-not that the blood itself believes, but that those born in that lineage have both the right and a special spiritual capacity to recognize, receive, and believe the truth. The term is simply a beautiful, a poetic, and a symbolic way of referring to the seed of Abraham to whom the promises were made. It identifies those who developed in pre-existence the talent to recognize the truth and to desire righteousness.’ (New Witness, pp. 38-39)” (McConkie and Millet, Doctrinal Commentary on the Book of Mormon, vol. 2, p. 61)
The Lord has made promises to the ancient prophets that the house of Israel will be redeemed in the last days. The Lord does this by grafting. He takes the wild branches of the mother tree and grafts them into these scattered natural trees. The interpretation of this is found in the next section.