Psalms 148:9

Mountains, and all hills - As being among the loftiest objects of earth, raising their heads highest toward the heavens.

Fruitful trees, and all cedars - Fruitful trees, not as distinguished from those which are barren, but as distinguished from forest-trees, those whose nature is that they do not bear fruit. Of the latter, the cedar was the most prominent, and, therefore, is made the representative of the whole.