Why did Aaron's staff turn into a serpent, and how did the magicians copy it?
The sign is a direct confrontation with Pharaoh-as-dragon on his own ground: the word used in Exodus 7 is not the ordinary word for snake but tannin, the Hebrew chaos-creature, and Ezekiel later identifies Pharaoh himself as 'the great tannin lying in the midst of his Nile streams' — Aaron's staff-dragon swallowing the magicians' staff-dragons is the whole contest in miniature.
Start with the word, because English translations hide the most important detail.
When Moses' staff became a snake at the burning bush (Exodus 4:3), the Hebrew word is nachash (נָחָשׁ, H5175) — the ordinary word for a snake, the same word used for the serpent in Eden. When Aaron throws down the staff before Pharaoh in Exodus 7:10, the text uses a completely different word: tannin (תַּנִּין, H8577). The ancient Greek translates it drakōn — dragon. English translations commonly render both words "serpent" and lose the escalation entirely.
Tannin is not a garden snake. It is the great sea-creature of the Hebrew imagination: one of the tanninim created on the fifth day of creation (Genesis 1:21), the monster YHWH slays at the sea (Isaiah 27:1), the creatures whose heads God crushed in the waters in the great retelling of the Exodus in Psalm 74:13. And centuries after the plagues, Ezekiel makes the identification explicit when he delivers an oracle against Egypt:
Behold, I am against you, Pharaoh king of Egypt, the great tannin lying in the midst of his Nile streams. (Ezekiel 29:3)
Pharaoh is the great tannin of the Nile. When Aaron's staff becomes a tannin in the throne room, it is not a nature trick to impress an audience — it is a direct confrontation with the dragon on his own ground. The sign says: here is another dragon, and we will see whose dragon is stronger.
The magicians do replicate the sign. The text says they did so "by their secret arts" (Exodus 7:11), and the men performing the signs are the chartummim (חַרְטֻמִּים, H2748) — Egyptian professional diviners who first appear in Genesis when they fail to interpret Pharaoh's dreams and Joseph succeeds. They produced their own tannin-staffs. The text does not explain the mechanism, and it is not the point of the narrative to explain it. Ancient Egypt had a tradition of snake-charming by pressure on the back of the neck, but the narrative is not offering a naturalistic account — it is staging a contest of powers.
Then comes the verdict: Aaron's staff swallowed their staffs (Exodus 7:12). The verb is bala (בָּלַע, H1104), to swallow or devour — not merely consume but overwhelm. It is the same verb used when the earth swallowed Korah's company in the wilderness (Numbers 16:32), and the same verb used at the Song of the Sea: "you stretched out your right hand; the earth swallowed them" (Exodus 15:12). The first sign of the plague cycle and the final act of judgment at the sea use one verb. Aaron's staff swallowing the magicians' dragon-staffs is the sea swallowing Pharaoh's army in miniature, staged before the plagues begin.
The magicians manage to replicate the first two plagues as well — blood and frogs — but cannot make gnats (plague three), and at that point they confess: "This is the finger of God" (Exodus 8:19). By plague six they cannot even stand before Moses, struck down by boils themselves (Exodus 9:11), and they vanish from the story. The same pattern repeats in Daniel's Babylon, where the same caste of court diviners (called by the same Hebrew title) fail where God's servant succeeds. Paul, writing to Timothy, names two of the Exodus magicians — Jannes and Jambres — as a type of those who oppose the truth in the last days (2 Timothy 3:8).
The dragon-thread runs to the end of the canon. The great dragon cast down in Revelation is called "that ancient serpent" (Revelation 12:9; 20:2) — the Pharaoh-dragon of the Nile, opened out into the last anti-God power. Aaron's staff swallowing the magicians' staffs in Pharaoh's throne room is the first scene of a confrontation the Bible does not finish until the last pages.
Did God harden Pharaoh's heart, or did Pharaoh harden his own?
Both — and the Hebrew grammar shows each one precisely, with God forecasting the hardening before it begins and Pharaoh acting as his own agent through the first five plagues before God becomes the explicit subject at plague six.
What does Romans 9 mean by 'he hardens whom he wills'?
Paul is drawing a direct theological principle from the Exodus plague cycle, reading the Greek of Exodus 9:12 and 9:16 together: the same God who made Pharaoh's heart firm for the display of his name makes the same move in every age, and Paul says so using the same Greek verb the Septuagint used for the hardening of Pharaoh.
When did God start hardening Pharaoh's heart?
God forecasted the hardening before plague one (Exodus 4:21 and 7:3), but the first verse in the narrative where YHWH is the explicit grammatical agent of the hardening is Exodus 9:12, the sixth plague — before that, the verbs are either intransitive or show Pharaoh as his own agent.
Why did God turn the Nile into blood?
The plague targets Egypt's source of life and divine status — the Nile was deified in Egyptian religion — and the stated purpose in Exodus 7 is not punishment for its own sake but forcing Egypt to know who YHWH is, answering Pharaoh's own boast that he does not know YHWH.