Mount up with birds

Vishnu and Garuda

“ They that wait upon the Lord shall renew their strength; they shall mount up with wings as eagles." (Isa. 40: 31) 
Probably the birds, denoting symbolically the angels, symbolise certain spiritual hierarchy.
And often birds participate in struggle of the angels against the demons. That is, the opposition between higher and lower states. In the Hindu tradition this is the struggle of the Devas against the Asuras and also, the combat of Garuda against the Nāga. The Garuda is the vahana of the God Vishnu usually and is the eagle, who regarded by many cultures as the 'sacred messenger'. The birds thus played the part of “messengers” and assist in matters of higher knowledge.  For example, the dove as spirit messenger bringing communication between the realms of the conscious and the unconscious.
Many Hindu gods such as Lakshmi, Brahma, and Kama are portrayed riding upon peacocks. According to Sufi legend the original Spirit was created in the shape of a peacock. When it saw itself in the mirror of the Divine Essence it was so overwhelmed by the beauty it saw therein that great drops of sweat flew from its body. It was taught that from these drops all other living creatures were formed. They are sometimes seen drinking from Eucharistic chalices or near the Tree of Life. Because of their association with the Tree of Life, peacock thrones were popular in ancient Babylon and Persia.
 Birds in general represented the element air, but at the same time, their flight was identical to the ascension to heaven. And the phoenix also incorporated the element fire, thus portraying the union of two elements and its transformative – regenerative – outcome. The phoenix bird builds its nest which at the same time is its funeral pyre, and then setting it alight cremates itself. But it arises anew from the ashes transformed. The birds of alchemy - the Black Crow, White Swan, Peacock, Pelican, and Phoenix - which are descriptive of certain stages of the alchemical process. Thus, in Phenix we have captured the alchemists experience of spiritualisation, that he is no longer dependent upon his physical body as a foundation for his being.
For hindus this stage can be symbolised by a swan - hamsa. White swan is the vehicle of Saraswati, the goddess of knowledge and wisdom. Paramahamsa (supreme swan from sanskrit) it's a symbol of spiritual perfection and this title of honor is applied to teachers who can always distinguish between the Real (so) from the unreal (ham).
And what means a condition of a bird for the person which has not reached this stage?
In medieval 'Book of Beasts' translated by Terence White we read:

...when the eagle grows old and his wings become heavy and his eyes become darkened with a mist, then he goes in search of a fountain...and he dips himself three times in it and he is renewed with a great vigour of plumage and splendour of vision...Do the same thing, O Man, you who are clothed in the old garment and have the eyes of your heart growing foggy. Seek for the spiritual fountain of the Lord...

Cathedral of S Lorenzo, Genova