Enos had likely learned from his grandfather Lehi, his uncle Nephi, and his father, Jacob, that the Nephites would eventually turn from the truth, sin, and be destroyed. Because that was the apparent future scenario, he desired that God would preserve the record of his people for his brethren, the Lamanites, so they could in some future day be brought to salvation. That is one of the purposes of the Book of Mormon. Its preface states that it is “written to the Lamanites,” and Doctrine and Covenants 3:20 says the plates were preserved “that the Lamanites might come to the knowledge of their fathers, and that they might know the promises of the Lord, and that they may believe the gospel and rely upon the merits of Jesus Christ, and be glorified through faith in his name, and that through their repentance they might be saved.”
Enos, along with his prophet-forefathers, asked with faith and received assurance from the Lord that he would preserve the records and eventually get them into the hands of the Lamanites. Again, the Nephites sought to reclaim the Lamanites without success. The baseness and brutality of the latter was frightening.