Tillich on symbols

A symbol (e. g. a flag), unlike a sign (e. g. a street sign), has qualities of what it points to. Symbols are born and die; signs are consciously invented and removed.
The main function of the symbol is to open up the soul to otherwise hidden levels of reality that cannot be grasped in any other way. A symbol is (unconsciously) appropriate to a group on account of the inner situation of that group.
The depth dimension of reality is the ultimate one, underlying every other, it is the dimension of the Holy. The wholly transcendent is beyond the infinite variety of material that may be used to symbolize it. Symbols are meaningful on account of their relationship to the ultimate. There is an idolatrous tendency to confuse the symbol (e. g. a holy person, book, doctrine, or ritual) with the ultimate.
The transcendent level "in" a symbol is

ultimate reality, being itself, the ground of being, the power of being, being itself, being as being;

the qualities attributed to God -- love, mercy, power, omniscience, omnipresence -- are taken from experienced qualities we have ourselves and cannot be literally applied to God;

if the acts attributed to God are not interpreted symbolically, they misleadingly seem to imply an ordinary substance doing things in space and time.

The immanent level of the symbol includes

the incarnations of the divine;

the symbolic sacrament (greater than the literal interpretation);

symbolic thins used in ritual and aspects of architecture.

The truth of a religious symbol is not an empirical matter, though it does not depend on the continuation of the situation in which the symbol was created -- for example,

Mary -- no longer needed now that we realize that we can relate to God without any need for intermediaries;

Joseph, whom we must regard as the real father of Jesus if Jesus is to be fully human as he must be for faith; and

the cross -- a symbol that subverts the tendency toward idolatry.