Music
Music has always been used in religious contexts; it is fundamentally associated with emotions. ("The art of emotions par excellence," according to Dream Analysis Part I, p. 11.) In everyday life, bad thoughts can be chased away by music, and more metaphysically, so can evil spirits. Music also establishes a sense of community, whether it involves mutual music taste, religious ceremonies, or chanting supporters—everyone feels the same and shares an emotional experience.
Furthermore, music helps one establish contact with the deeper self on one hand, and on the other, music is an expression of the deeper self.
In dreams, music often appears as an expression of eros, the relational function. For example, the absence of (expected) music can express the absence of eros; music, joy, and companionship can symbolize harmony with oneself and others.
Of course, music is a primordial result of human creativity, undoubtedly one of the first arts for humankind. But it is also an invisible art and, along with the other mentioned qualities, forms a bridge to the invisible world.