I was asked why the language of Mosiah 18: 8-10 related to membership in the church, and not to others outside the church. Here’s my response.
These verses are talking about entering into a covenant and becoming “the fold of God.” (Verse 8.) This fold will be “called his people.” (Id.) The fold, who have this covenant, and who are called His people, are to be “willing to bear one another’s burdens, that they may be light.” (Id.) The whole passage is relating to the interrelationship between those who are of the covenant, the fold, and who are God’s people as a result of this covenant. These are the duties owed internally to the fold.
It continues to explain that these people should be “willing to mourn with those that mourn.” (Verse 9.) The word “those” should be read in the context of the covenant, the fold, the people and the obligation arising from within the group.
These verses are church/fold/covenant people related, and govern the obligations which those who come into that fold owe to each other. It arises out of the covenant of baptism. (Verse 10.)
The obligation owed within the church membership to one another on the one hand does not eliminate other obligations owed to your fellow man. Indeed, it is one of the chief obligations owed to all humanity to cry repentance and bring others into the fold. Christ also extended the obligation to care for others without regard to their status, including in His parable of the good Samaritan. So to say there is one duty owed within the church is not to say there are not other obligations owed to others outside the church.