The eagle has been associated with the belief in renewal or rebirth. In a fragment of an ancient Babylon text, there is the story of King Erana being taken to the heavens on the wings of an eagle. It was a widely used custom in many ancient cultures to release eagles at the funeral of a ruler: the flight of an eagle, as the body was cremated, symbolized the departure of the soul to live among the gods. In Palmya, in ancient Syria, the eagle was associated with the sun-god; and thought capable of rejuvenation like the phoenix. As a killer of snakes and dragons, the eagle represents the victory of the light forces over the dark. The positive traits of this kingly bird are energy, renewal, contemplation, acuity of vision of vision, and royal heritage which substantiates it being an attribute of the god Jupiter.
In Christian iconography the eagle is often seen to symbolize John the Evangelist, the ascension of the prophet Elijah, and the ascension of Jesus Christ. The eagle’s ability to fly high is why it symbolizes Christ’s ascension and is frequently depicted on baptismal founts.
The eagle’s alchemical symbolism can readily be recognized in that the goals of alchemy are the transmutation of base (impure) metals or spirits into more purer or finer ones. This called for the destruction of the base metals to release the spirit and the renewal or reunion of the spirit in the new one. This is a renewal process, the death one the one and birth of the new, symbolized in the eagle. The eagle is thought as a royal bird as alchemy was called the royal art.
In its psychological association the eagle shares and opposite symbolism which can be reversed through personal effort. Being symbolic of St. John the evangelist most firmly established in the intellectual realm, the eagle symbolizes the height of intellectual activity; however, this bird also can represent the degrading, consuming passion, of the intellect, which causes humans not to be ruled by the mind but the body. The eagle displays such behavior when he interrupts his elegant flight to swoop down on his prey to satisfy his carnal needs. At times humans behave the same way, their passions control them. This is the reason the eagle symbolized Adam, the first man, in medieval bestiaries: Adam, too, who originally dwelt close to heaven, lost his glory when sighting the forbidden fruit. Humankind like the eagle can improve its status by returning to the intellectual realm. This also has alchemical symbolism: when an experiment failed the alchemist had to start over again. A.G.H.
Biedermann, Hans. Dictionary of Symbolism: Cultural Icons and the Meanings Behind Them. (Transl. by James Hulbert). New York. Facts On File, 1992. p. 108-110.