3Ne Ch12

Jesus sets apart the Twelve who represent the apostles for the Nephites right before giving a sort of Sermon on the Mount to the Nephites. The Beatitudes are spoken and he teaches the new law now that the law of Moses is fulfilled just like it is done in Matthew 5 of the Holy Bible.
The ones that were chosen to have authority to baptize were presented to the people and called to be their church leaders and servants to minister to everyone and preach the word of God while baptizing any who believed and repented (v1-2). then there is the section that starts out similar to Matthew 5 with the Beatitudes: Be Humble, Be Prayerful, Be Smart, Be Grateful, Be Merciful, Be True, Be Clean, and so on...there are several interpretations of the verses and what is means (v3-11). If you are those things, you will be blessed and have great joy, being the salt of the earth that will be good for nothing if it loses it's flavor (v12-13). The righteous are set up to be a light to others and that cannot be hidden and shouldn't because we should glorify the Father with our good works and shine before others (v14-16).
Christ then speaks of the law of Moses, it is not destroyed but fulfilled in Him making the rules change slightly to repenting and coming unto Christ with broken hearts and contrite spirits so the people can be saved through His sacrifice (v17-20). Here is the before and after changes of the Law of Moses.
                  Before                                                    After
v21-26) Thou shalt not kill:                             Don't even be angry or judgment will come, reconcile!
v27-30) Thou shalt not commit adultery:         Don't even think lustful thoughts or you've already sinned
v31-32) Divorce is okay:                                Divorce is NOT okay except if you fornicate unlawfully
v33-37) Perform all thine oaths unto the Lord:  Don't swear at all upon anything
v38-42) An eye for an eye:                             Don't sin against others even if they have against you
v43-45) Love thy neighbor, hate thine enemy:    Love your enemies and pray for them

The Lord has set forth these new laws to help us be perfect like He and our Father is so we are ready to live with them in heaven after our resurrection (v46-48).  It may seem stricter because it is, more is expected by the Nephites and even by us because we have the proof of Christ's coming.