Alma 19

After their conversion, Lamoni and his servants -

"...did all declare unto the people the selfsame thing—that their hearts had been changed; that they had no more desire to do evil.
(Book of Mormon Alma 19:33)

And -

"...as many as heard his words believed, and were converted unto the Lord." (Book of Mormon Alma 19:31)

And -

"...there were many that did believe in their words; and as many as did believe were baptized; and they became a righteous people, and they did establish a church among them." (Book of Mormon Alma 19:35)

It seems at first that all that was necessary for these people was to hear the word, believe, experience a change of heart, and be baptized and they would remain thereafter a "righteous people". But later after Ammon had freed Aaron and his brethren in Middoni -

"...Ammon and Lamoni returned from the land of Middoni to the land of Ishmael..." (Book of Mormon Alma 21:18)

For as Aaron tells King Laman -

"...the Spirit of the Lord has called him another way; he has gone to the land of Ishmael, to teach the people of Lamoni." (Book of Mormon Alma 22:4)

It becomes clear that it was necessary to continue to teach the people by the Spirit -

"Wherefore, I said unto you, feast upon the words of Christ; for behold, the words of Christ will tell you all things what ye should do." (Book of Mormon 2 Nephi 32:3)

Lamoni then -

"...caused that there should be synagogues built in the land of Ishmael; and he caused that his people, or the people who were under his reign, should assemble themselves together." (Book of Mormon Alma 21:20)

"And Ammon did preach unto the people of king Lamoni; and it came to pass that he did teach them all things concerning things pertaining to righteousness. And he did exhort them daily, with all diligence; and they gave heed unto his word, and they were zealous for keeping the commandments of God." (Book of Mormon Alma 21:23)

It becomes clear that it is necessary that we continue to "hear the word" and give heed to it "daily" in all diligence to stay in the way and remain a righteous people.