The Moon is associated with subconscious fears, darkness, secrets, mistakes and mood swings. The High Priestess is the female principle, passive, secretive and receptive. She represents hidden knowledge, mysteries, intuition and is associated with the Moon and its phases. With this pair nothing is open and out in the light and there’s nothing rational, harmonious or easy.
The elements of the cards are Water (Moon) and Water (High Priestess). The elements are neutral and rather friendly to each other, but they can lead to excessive passivity or inertia, trying to maintain what's already there, reluctant to make a drastic move.