2 Nephi 5:27
27 And it came to pass that we lived after the manner of happiness.
What does this mean? What is the manner of happiness? Nephi certainly knew something about happiness from the dream he and his father shared:
1 Nephi 8:10
10 And it came to pass that I beheld a tree, whose fruit was desirable to make one happy.
There are other examples of people living happily in the Book of Mormon:
Alma 50:23
23 But behold there never was a happier time among the people of Nephi, since the days of Nephi, than in the days of Moroni, yea, even at this time, in the twenty and first year of the reign of the judges.
Why were the people happy at this time? What about this example:
4 Nephi 1:16
16 And there were no envyings, nor strifes, nor tumults, nor whoredoms, nor lyings, nor murders, nor any manner of lasciviousness; and surely there could not be a happier people among all the people who had been created by the hand of God.
In this case it's more clear that happiness is inversely proportional to wickedness, or rather, that it is directly proportional to righteousness.
Ammon the missionary seemed to have an extremely refined sense of happiness in his life. See Alma Chapter 19 as well as this latter example:
Alma 27:16-18
16 And it came to pass that as Ammon was going forth into the land, that he and his brethren met Alma, over in the place of which has been spoken; and behold, this was a joyful meeting.
17 Now the joy of Ammon was so great even that he was full; yea, he was swallowed up in the joy of his God, even to the exhausting of his strength; and he fell again to the earth.
18 Now was not this exceeding joy? Behold, this is joy which none receiveth save it be the truly penitent and humble seeker of happiness.
Notice that Ammon is described as being truly penitent and humble. This implies that he was always repenting, always retaining a remission of his sins. Always worthy of the companionship of the Holy Ghost. Always on the tipping point as far as joy and fulfillment were concerned. There's no doubt about his eventual destiny:
Mosiah 2:41
41 And moreover, I would desire that ye should consider on the blessed and happy state of those that keep the commandments of God. For behold, they are blessed in all things, both temporal and spiritual; and if they hold out faithful to the end they are received into heaven, that thereby they may dwell with God in a state of never-ending happiness. O remember, remember that these things are true; for the Lord God hath spoken it.
"Happiness" and "Righteousness" are scripturally synonymous!