When 'islands' are contrasted to 'earth' or 'mountains,' they signify the truths of faith, because they are in the sea. They signify doctrinal things which are rituals. 'Islands' signify peoples who are more remote from the worship of God. People who are steeped in the internal sense of the Word, such as angels, do not know what islands are, because they no longer have any concept of such places. Instead they have a perception of more remote worship, like the gentiles outside the church.

'Islands,' in Ezekiel 27:6, signify people in the church in a natural, materially-oriented state but still rational.

(Reference: Apocalypse Explained 406; Isaiah 1, Isaiah 49, 49:1)

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.