Joy of the saints
Enos tells us that the words his father, Jacob, taught him concerning eternal life and ‘joy of the saints’ sunk deep into his soul and caused his hunger to be forgiven of his sins.
Enos 1:3The word ‘saints’ is used 28 times in 27 verses in the Book of Mormon. The vast majority of these instances, however, reference tribulation and the Lord’s vengeance for those who spill ‘the blood of the saints’, ‘kill the saints’, or ‘destroy the saints’ (1 Ne 13:5, 9; 2 Ne 26:3, 5; 2 Ne 28:10; 3 Ne 9:5, 7–9, 11; 3 Ne 10:12; Mor 8:27, 41; Eth 8:22). Nephi also speaks of the saints as spreading abroad on the face of the earth (1 Ne 14:12, 14), Jacob tells us that God delivers his saints from death and hell (2 Ne 9:19); others prophesy or testify that graves were opened at the time the Savior was resurrected and the saints appeared to many (Hel 14:25; 3 Ne 23:9, 11). Mormon tells us that the saints shall cry from the dust through the coming forth of the Book of Mormon (Mor 8:23), speaks of the prayers of the saints (Mor 9:36), and tells us that the saints shall dwell with God after tribulation (Mor 8:26).
3 Behold, I went to hunt beasts in the forests; and the words which I had often heard my father speak concerning eternal life, and the joy of the saints, sunk deep into my heart.
Of all those who speak of the saints, however, Jacob is the only one to explicitly mention the saints in the context of joy or happiness (2 Ne 9:18, 43):
2 Nephi 9:18Interestingly, Jacob’s father, Lehi, teaches his children that the fruit of the tree was “desirable to make one happy” (1 Ne 8:10) and filled his soul with “exceedingly great joy” (1 Ne 8:12). Of course, these are the very words that Enos remembers Jacob using in the context of ‘joy of the saints’ and ‘happiness of the saints.’ And Nephi makes the connection from Enos' memory to Lehi's description complete by referring to those in Lehi’s dream that partook of the fruit as 'saints' (1 Ne 15:28).
18 But, behold, the righteous, the saints of the Holy One of Israel, they who have believed in the Holy One of Israel, they who have endured the crosses of the world, and despised the shame of it, they shall inherit the kingdom of God, which was prepared for them from the foundation of the world, and their joy shall be full forever.
2 Nephi 9:43
43 But the things of the wise and the prudent shall be hid from them forever--yea, that happiness which is prepared for the saints.
This brings Enos’ thirst after the ‘joy of the saints’ into the realm of the Tree of Life vision: He is in the wilderness, desires conversion and the joy and happiness the fruit brings, then desires for the conversion of his loved ones, just as Lehi and Nephi both did in the Tree of Life vision. It's also likely that Jacob experienced the same vision or something similar--consider that Nephi and Lehi both tell us that Jacob saw the Savior (2 Ne 2:4; 2 Ne 11:3) and Lehi tells us that Jacob has beheld "that in the fullness of time he [the Redeemer] cometh to bring salvation unto men" (2 Ne 2:3). This sounds like the extended vision of the Tree of Life vision that explains the Savior's mortal ministry.
Thus, the phrase ‘joy of the saints’ frequently used by Enos' father, Jacob, probably referred to the Tree of Life, whose fruit was seen by Lehi, Nephi, and (probably) Jacob, and brought joy and happiness to the saints. It shows the remarkable literary complexity in the Book of Mormon and argues for a spiritual/literary influence between Jacob and Enos--indeed, Lehi, Nephi, Jacob, and Enos--that becomes evident in the writings these men left behind.