The proud and lofty will be cut down in that day, the day of the Second Coming; cedars and oaks are symbolic of the proud and lofty. Mountains and towers are also symbols of the high and lofty. Verse 14 adds “and upon all the nations which are lifted up, and upon every people”—nations and people being parallel with mountains and hills.
The Greek Septuagint has one phrase from verse 16 and the traditional (Masoretic) Hebrew text the other phrase, but the Book of Mormon has both (see footnote 16a