Here the Savior gives the Nephite saints pragmatic advice for how they are to conduct their religious meetings. They are to meet together often. Because they are believers in a community, there will be others who are not believers, or who are not of the same community. The gospel is not to be exclusive. There is to be no turning away of any simply because they do not fit a definition of “one of us.” For the Nephites, the most obvious historical reference would be the Nephite/Lamanite relations. Should a Lamanite desire to come to one of these communal meetings of the believing Nephites, they should be accepted.
Significantly, the Savior punctuates this instruction with a reference to the Sermon and letting their light shine. As he told the twelve (verse 16), he is the ultimate light of example. We are to take his example and follow it ourselves, and in so doing become a light to our neighbors. We cannot be a light to others if we exclude them from our presence.
This inclusion/exclusion of non-believers has a wider significance for the Nephites than it does for modern saints. For us, this means that our religious meetings are open. For the Nephites, it meant that their communities should be opened to others. We already live in communities where peoples of different beliefs (both religious and political) are allowed. This particular Nephite group in Bountiful was most likely brought together based on their similarities after the destruction. They might have decided to exclude any who did not conform to the way they believed. They are told not to do that, and to be open to others. For them, this would necessarily require opening the community, else there couldn’t be anyone knowing of the religious meetings to even attempt to attend them.