Isaiah 14:29

Rejoice not thou, whole Palestina, because the rod of him that smote thee is broken: for out of the serpent’s root shall come forth a cockatrice, and his fruit shall be a fiery flying serpent.

It is a warning to all Philistia not to rejoice because the rod that struck it is broken, for a more venomous successor will rise in its place as part of God's pronounced judgments upon the nations.
The warning stands within the proverb against the king of Babylon, the Papal king of Mystery Babylon, whose earthly rulers served Lucifer, the day-star who inspired all her wickedness and rules behind that false religious system through sorcery and deceptive teaching.
The surrounding passage pictures that king's overthrow and descent to sheol in figurative language, where the dead are stirred up to rise and mock him with feigned obeisance, picturing death as silence, darkness and sleep rather than conscious souls conversing underground.
The cockatrice and its fruit are real flying, fiery serpents of the same kind as the burning serpents of Numbers 21:6, called seraphim for their bright, glowing, luminous appearance like the angelic seraphs.
So too the serpent in Eden was not originally a crawling reptile but a far more splendid, shining, glorious winged creature, one of the seraphim, subtle and sagacious beyond all beasts and chosen by Satan as his speaking medium, until after the curse it was degraded to crawl in the dust and can now only hiss.

Setting and Judgment Warning

Isaiah 14:29 belongs to the predictions concerning Palestina or Philistia found in Isaiah 13 to 16, grouped together with the predictions concerning Babylon and Moab. It stands among the judgments pronounced by God upon the nations, with Philistia included among the peoples facing those judgments. In that setting it foretells the overthrow and destruction of Babylon.

It belongs to a prophecy of God choosing Israel again the second time and giving them rest from sorrow and fear and the hard bondage wherein they were made to serve. It is part of the proverb to be taken up against the king of Babylon, who is the Papal king of Mystery Babylon. After the Lord has broken the staff of the wicked and the sceptre of the rulers, him who smote the people with a continual stroke and ruled the nations in anger, the whole earth is at rest and quiet and breaks forth into singing. God's people, figured as the fir trees and the cedars of Lebanon, rejoice that since he is laid down no feller has come up against them.

The chapter containing the verse is a prophecy concerning Babylon and its highest king, Lucifer, and it presents God's refuge from Babylon's doom. The prophecy of Babylon rises from the earthly king of Babylon to Lucifer, the day-star, the son of the morning, who has inspired Babylon in all her wickedness. Lucifer is presented as the King of Babylon because the earthly rulers of Babylon served him. Its context identifies Satan as the ruler behind Babylon, the false religious system, and associates that system with sorcery and deceptive teaching that poisons the nations, with its rule and influence continuing through the system's laws and subjects.

Babylon's Fall Pictured Figuratively

The passage from Isaiah 14:4 to 14:30 portrays the overthrow of the king of Babylon and his going down to sheol in the nether parts of the earth. There the dead are stirred up to meet him, and the conquered kings are pictured as rising from their thrones in that dark abode to meet him with feigned obeisance and taunts. Their conversation and actions in mocking the fallen ruler are figurative language, not a literal account of conscious dead people seated on thrones and conversing together in an underground abode. It pictures the dead in silence, darkness and sleep.

Their speech no more means the dead are alive and conscious than slaughtered soldiers with swords under their heads are literally comforted. Nor does it prove consciousness any more than Rachel literally wept nearly two thousand years after her death.

Fiery Flying Serpent

The verse describes a real flying, fiery serpent, showing that flying serpents exist. It is of a similar species and the same kind as the fiery or burning serpents in Numbers 21:6. Those serpents are called seraphim, likely named for bright, glowing appearance, whose resplendent, luminous, burning, glowing color resembles the angelic order also called seraphs or seraphim.

The verse supports that the serpent in Eden was not originally an ordinary reptile or crawling reptile. It was a far more splendid and beautiful, luminous, shining, glorious, winged creature, one of the seraphim, appearing as a messenger from the upper world. It was gentle and innocuous before the fall, moving by wings or with head and breast elevated above the ground. Scripture calls serpents seraphim because they are the offspring of the old serpent.

The Hebrew nachash means close scrutiny or enchantment and is kindred to seraph, meaning shining and glistening like polished brass. The Eden serpent was more subtle, meaning crafty and prudent, knowing and sagacious beyond all beasts of the field, and Satan chose this high, attractive speaking medium. After the fall and curse it was degraded to crawl in the dust, eating what is mixed with dust, and now can only hiss.