Anti-Nephi-Lehi proclaims that should they take up arms again, they would no longer be abele to be atoned by Christ. Once again we again we have a text that would be problematic in a different context. There is no doctrine that would suggest that the atonement does not apply to those who defend themselves. There is, however, doctrine which tells us that the atonement cannot cleanse of from murder (DC 42:18). Anti-Nephi-Lehi has persisted in classifying their former sin as “murder.” Nevertheless, it was forgiven once, why not a second time? The difference is in the knowledge of the people. As part of their prior life, their actions were considered normal, and were even expected. Their new perception through their newly forgiven sight now places those actions in a completely different category. Now they know that they should not kill in hatred, or for a religious zeal. In their converted state, what was previously forgivable becomes unforgivable.
Vocabulary: In this context, “retain” is used in the sense of holding back. They are not “retaining” their swords in the sense of maintaining possession, but rather they were restraining them from use.