It is interesting that the secret combinations were more successful among the Nephites than the Lamanites (vv. 20–21). Since the righteousness of the Lamanites did exceed that of the Nephites (see 6:1 above), the Nephites were more susceptible to Satan (v. 21). The devil takes power when commandments are broken (see TPJS, 181).
We notice the similarities but yet the contrast between the church and the secret combinations. The church members entered into sacred covenants and oaths. Secret combinations have their secret covenants and oaths (v. 21). Church members should be willing to lay down their lives for a brother or sister in the gospel (see 1 John 3:16). Secret combinations protect their fellow members who have murdered (Helaman 6:21). the church member recognizes fellow members as brothers and sisters in the gospel and calls them his brothers and sisters (see Matthew 12:49–50). The band of robbers had secret signs and words to recognize and protect a brother in his wickedness (Helaman 6:22–23). The church members believed “in obeying, honoring, and sustaining the law” (Articles of Faith, 12). The Gadianton band followed the laws of their wickedness but lived contrary to the just laws of their country and their God (Helaman 6:23–24). Thus, they followed Satan rather than Christ.