The Book of Mormon scripture, Mormon 3:18, says that the twelve tribes will be judged by the twelve Jesus chose to be His disciples in the land of Jerusalem. Does this include Judas as we have been taught he is not to be saved? Surely it can’t refer to Mathias as he replaced Judas after Jesus had gone — I’m confused.
The term “judged” in that scripture does not mean “condemned,” but means “to pass judgment on.” And where it mentions the twelve tribes, it refers to all the descendants of Abraham, Isaac and Jacob, who make up the Twelve Tribes of Israel. In verse 19 of that same scripture Mormon states that all of the Nephites and Lamanites, who are also members of the House of Israel, will be judged by the twelve disciples that Jesus chose when he visited the Americas following his resurrection.
So the twelve disciples chosen by Jesus at Jerusalem will pass judgment on Judas and on Mathias and on everyone else in that chosen lineage, except for the Nephites and Lamanites, whose judgment has been delegated to the twelve that Jesus chose in the Promised Land, as mentioned above.