The key, or clavicle, symbolizes access to something that has been hidden.
Keys can lock or unlock.
Gods holding keys symbolizes a need to keep something private or occluded.
Magic charms or talismans can be keys.  Examples are key charms and skeleton keys.
A key symbolizes power given to someone, e.g. keys to the city.
They can be important to cultural rituals to honor old knowledge or to carry one into new information.  Examples are Ceremony of the Keys in London and the Girl Scouts initiation ceremony.
They can be buried with people to open the gates of the underworld.
Peter held the keys to the Pearly Gates of Heaven
Crossed keys, where one key is gold and one key is silver symbolize:
—golden key = golden sun, male power, to bind or release in heaven
—silver key = silver moon, female power, to bind or release on earth

image link

Crossed Keys of Janus
In ancient Roman religion and myth, Janus is the god of beginnings, gates, transitions, time, duality, doorways, passages, and endings. He is usually depicted as having two faces, since he looks to the future and to the past. The crossed keys symbol was associated with the Roman God Janus and the primordial deity Zurvac, who were both gods of time, remover of obstacles and keepers of doorways.

From plotinus.com The opening month of the year (January, from janua, “gate”) was sacred to [Janus], as was the first day of each month. He presided over the start and the vestals took care of the completion of any enterprise. He ruled the birth of gods, the cosmos, mankind and its undertakings. As warden of gates, which he opened and closed, he was depicted with a doorkeeper’s keys and staff. His two faces meant that he watched entrances as well as exits, and saw into the internal as well as the external world, left and right, above and below, before and after, for and against. His shrines were archways, such as gateways or arcades at crossing places.

Pope’s Crossed Keys (wikipedia image)

Crossed Keys of the Pope
wikipedia says The insignia of the papacy includes the image of two Crossed Keys, one gold and one silver, bound with a red cord. This represents the “keys to the Kingdom of Heaven” (Matthew 16:19; cf. Isaiah 22:22) and is in many ways the quintessential symbol of the Papacy as an institution and of its central role within the Catholic Church. Jesus’s statement to Simon Peter, “whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven”, is understood in Roman Catholic theology as establishing two jurisdictions, Heaven and Earth; the silver and gold keys are said to represent these two jurisdictions. The silver key symbolises the power to bind and loose on Earth, and the gold key the power to bind and loose in Heaven (another interpretation says that the silver key represents “binding” and the golden key represents “loosing”).

Keys don’t have to be a literal key. They can take other forms.

CODES

Hammurabi’s Code

Hammurabi’s Code. The Hammurabi code of laws, a collection of 282 rules, established standards for commercial interactions and set fines and punishments to meet the requirements of justice. Hammurabi’s Code was carved onto a massive, finger-shaped black stone stele (pillar) that was looted by invaders and finally rediscovered in 1901.

Rosetta Stone

Rosetta Stone. The Rosetta Stone is a granodiorite stele, found in 1799, inscribed with three versions of a decree issued at Memphis, Egypt, in 196 BC during the Ptolemaic dynasty on behalf of King Ptolemy V. The top and middle texts are in Ancient Egyptian using hieroglyphic script and Demotic script, respectively, while the bottom is in Ancient Greek. As the decree has only minor differences between the three versions, the Rosetta Stone proved to be the key to deciphering Egyptian hieroglyphs, thereby opening a window into ancient Egyptian history.

SACRED WORDS from Everyday Health:

Om is a mantra and sacred word of Buddhists, Indians and anyone who’s ever practiced yoga. It’s thought that Om was the first sound that began Creation, the aural representation of Brahman and absolute reality.

Amen is considered one of the most sacred words in Christianity. the meaning of amen in Christianity to evoke affirmative truth, sincerity and solemnity. Amen isn’t a word solely restricted to Christianity, however. Egyptians worshipped a god called Amen-Ra, and the Amen within his name meant “hidden” and “unseen”. Within this context, both the word and the god Amen were understood to be invisible and inscrutable by mortal eyes, permanent and ever-present throughout time.

Allah represents the omniscient, omnipotent god that governs all Muslims.

Shalom means the act of completeness, perfection and fullness.  This is often extended into prosperity in the non-financial sense, tranquility, health, and harmony.

Yahweh This sacred word appears in the Old Testament well over six thousand times, making it the most commonly used form of God’s name. It is so revered by Jews, however, that it is too holy for them to speak aloud.

Despite the dozens of different religions practiced throughout the world, the presence of so many different sacred words unifies all believers in their quest to reject the distractions of daily life and achieve true, reverent peace.