The Lord's love is the sun of heaven, and it is natural for us to look above ourselves to the sun of this world in thinking about the Lord. It follows, then, that to be closer to the Lord we would climb into the highest places -- and indeed, people have been worshiping on mountains for ages. In fact, even steeples on modern churches are symbolic mountains. It makes sense, then, that a mountain in the Bible represents love to the Lord, the highest, purest love we human beings can experience. Mountains can also represent the desire for good that comes from the love of the Lord. Hills, meanwhile, represent a love of other people and a caring for them, and when "mountains" is used in the plural it generally represents both loves.

798. 'From fifteen cubits upwards the waters prevailed and covered the mountains' means that no trace of charity remained; and 'fifteen' means things so few as to be scarcely any at all. This becomes clear from the meaning of the number 'five', dealt with in Chapter 6:15. There it was shown that in the style of the Word, that is, in the internal sense, 'five' means those that are few. And since the number fifteen is the sum of five, which means few, and of ten, which means remnants, as has been shown at 6:3, this number has regard to remnants, which with those people were hardly anything at all. For so great were the persuasions of falsity that they did away with everything good. With regard to the remnants residing with man, the false assumptions, as stated already, and still more the persuasions of falsity, were of such a nature with the people before the Flood that they shut in and shut away remnants so completely that they could not be brought out. And if they had been brought out they would have been falsified in an instant. Indeed the life inherent in persuasions is such that it not only rejects everything true and soaks up everything false, but also perverts any truth that goes near it.