“Wherefore” recapitulates the theme of Yahweh’s mercies. Because we know him as merciful, we are willing to approach him and beg for that mercy which comes through the Atoning Messiah. Therefore Jacob exhorts us to be reconciled to the Father through the Son. (See commentary accompanying Jacob 4:5.) Such faith is effective even before Jesus performs the atonement. Yahweh’s covenantal promise that the atonement will be made allows it to be operative even before it is accomplished, an absolutely essential factor, for there is no repentance without the atonement. Jacob asks his people to take advantage of an atonement that has not yet happened but which is the only way that humankind can be saved.
Reference: The language that Jacob employs is very similar to Paul’s in Romans 5:2: “By whom also we have access by faith into this grace wherein we stand, and rejoice in hope of the glory of God.” While Jacob’s meaning is certainly the same, the similarity in the wording is no doubt influenced by Joseph Smith’s knowledge of the King James Version—not that Joseph Smith copied the phrase but rather that he used the terms familiar to him from his knowledge of the King James passage.