The Hebrew word śārāp̄ appears seven times in the Old Testament and is used to describe both a serpent and a class of supernatural beings (seraph/seraphim).
References to a serpentine figure occur in Numbers 21, Deuteronomy 8, and Isaiah 14/30.
In Numbers 21, the nation of Israel, evidently removed long enough from the miracle of the Exodus to start complaining about God’s provision, are beset by “fiery serpents” (Numbers 21:6, KJV) or “poisonous snakes” (NLT) that mortally wound the rebellious people. In the following verses, Moses is instructed by God to set a likeness of the fiery serpents upon a pole with the assurance that “Those who are bitten will live if they simply look at [the snake/pole]!” (Numbers 21:8, NLT).
In Deuteronomy 8, the word is then used when Moses relays God’s call for the people to remember how they had been faithfully led through the “terrifying wilderness with poisonous snakes and scorpions” (Deuteronomy 8:15, NLT).
The final uses of the words seraph/seraphim are in Isaiah where it is deployed sometimes symbolically, sometimes literally, in three different instances.
This begins in Isaiah 14 where God issues a warning to Philistia, a nation celebrating the death of Judah’s King Ahaz, the term is used to say, “From that snake [meaning Ahaz] a poisonous snake [meaning Hezekiah] will be born, a fiery serpent [seraph] to destroy you!” (Isaiah 14:29, NLT). The nation of Judah had suffered greatly during the unrighteous rule of Ahaz (2 Kings 16) but would be reconciled to God under the rule of Hezekiah who, as prophesied, would conquer the Philistines “as far distant as Gaza and its territory, from their smallest outpost to their largest walled city” (2 Kings 18:8, NLT).
“The Hebrew word śārāp̄ appears seven times in the Old Testament and is used to describe both a serpent and a class of supernatural beings.”
Continuing on, in Isaiah 30, the word is used to describe the dangerous and foreboding beasts in the wilderness around Egypt as God warns Judah of the coming consequences for its treaty with Pharaoh. 
Finally, and likely, the most well-known use of “seraph/seraphim” is the one recorded in Isaiah’s vision:
“In the year King Uzziah died, I saw the Lord. He was sitting on a lofty throne, and the train of his robe filled the Temple. Hovering around him were mighty seraphim, each with six wings. With two wings they covered their faces, with two they covered their feet, and with the remaining two they flew. In a great chorus they sang, ‘Holy, holy, holy is the Lord Almighty!’…Then one of the seraphim flew over to the altar, and he picked up a burning coal with a pair of tongs. He touched my lips with it and said, “See, this coal has touched your lips. Now your guilt is removed, and your sins are forgiven.” (Isaiah 6:1-3, 6-7, NLT)
As with cherubim, I believe seraphim are distinct from angels. Should we link cherubim and seraphim together as the same basic type of supernatural being? The description of seraphim being serpent-like seems distinct enough to separate the two from one another as does, in my mind, their functions. While the cherubim function almost as massive, terrifying signals of a divine presence, the seraphim seem to act as markers of divine judgment/action.
“The most well-known use of ‘seraph/seraphim’ is the one recorded in Isaiah’s vision.”
The linguistic ties of the word seraph to that of a poisonous, burning, fiery serpent seem to signify that a divine enactment has occurred or is about to occur, and the participant will either be found worthy or dead—much like the refiner’s fire in Malachi 3 and 1 Corinthians 3, a thing or person who has come to test someone’s work. In each usage of the term seraph, Israel, Judah, Philistia, or Isaiah is being tested. For some that judgment proves fatal, while for others it is cleansing. The presence of the seraphim signifies that process, that divine judgement.
Whether we’re discussing cherubim, seraphim, or angels, it’s clear there is plenty of room for interpretation. However, it should be noted that each being serves its purpose in God’s narrative, aiming to demonstrate God’s pursuit and purposes for his people, his prized creation: us. And while the presence of cherubim, seraphim, and angels might be unclear, the goodness of the God they serve/represent is not.
