Why does God seem different in the Old Testament and the New?
Text and context

This question usually smuggles in an assumption worth naming first: that "different" means "inconsistent" or "two gods." The texts on offer here don't support that reading, but they do show real development — and the difference between development and contradiction is the whole question.

Start with what stays fixed. Isaiah 46:9 has God declare his own singularity and continuity: "I am God, and there is none like me." That is not a claim about mood or method; it's a claim about identity across time — "remember the former things of old" presupposes the God remembering them is the same one acting now. Nehemiah 9:32, a prayer surveying centuries of Israel's history — kings, exile, Assyria — addresses one God as "the great, the mighty, and the awesome God, who keeps covenant and loving kindness" precisely because the covenant-keeping is what holds the story together despite its violent swings.

What does change is covenant administration — the terms under which God relates to his people at a given point in redemptive history. Deuteronomy 4:34 recalls Yahweh acting through plagues, war, "great terrors" to constitute a nation by rescue and law. Hebrews 8:13 explicitly names a covenant "obsolete" — Greek πεπαλαίωκεν (from παλαιόω, Strong 3822), "has made old" — and says the old is "near to vanishing away" (ἀφανισμοῦ). That is the New Testament's own account of why the terms shift: not that God became different, but that the covenant did, on the way to something it was always aimed at. Hebrews doesn't say the old covenant's God was harsher or lesser — it says its structure, sacrifice repeated yearly, was provisional, built to expire.

Watchman Nee's line, though written about the individual believer's history rather than Israel's, states the same shape in miniature: "Our old history ends with the cross; our new history begins with the resurrection." A hinge, not a break in identity.

Jeremiah 2:11 supplies the real contrast scripture cares about — not Old Testament God versus New Testament God, but the true God versus every substitute "which really are no gods." That's the line the text actually draws.

Isaiah 46:9 WEB
Remember the former things of old; for I am God, and there is no other. I am God, and there is none like me.
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See also 5
  1. Isaiah 45:21 Declare and present it. Yes, let them take counsel together. Who has shown this from ancient time? Who has declared it of old? Haven't I, Yahweh? There is no other God besides me, a just God and a Savior. There is no one besides me.
  2. Isaiah 42:9 Behold, the former things have happened and I declare new things. I tell you about them before they come up."
  3. Isaiah 46:5 "To whom will you compare me, and consider my equal, and compare me, as if we were the same?
  4. Psalm 111:4 He has caused his wonderful works to be remembered. Yahweh is gracious and merciful.
  5. Deuteronomy 33:26 "There is no one like God, Jeshurun, who rides on the heavens for your help, in his excellency on the skies.
Deuteronomy 4:34 WEB
Or has God tried to go and take a nation for himself from among another nation, by trials, by signs, by wonders, by war, by a mighty hand, by an outstretched arm, and by great terrors, according to all that Yahweh your God did for you in Egypt before your eyes?
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See also 5
  1. Deuteronomy 26:8 Yahweh brought us out of Egypt with a mighty hand, with an outstretched arm, with great terror, with signs, and with wonders;
  2. Deuteronomy 5:15 You shall remember that you were a servant in the land of Egypt, and Yahweh your God brought you out of there by a mighty hand and by an outstretched arm. Therefore Yahweh your God commanded you to keep the Sabbath day.
  3. Exodus 6:6 Therefore tell the children of Israel, 'I am Yahweh, and I will bring you out from under the burdens of the Egyptians, and I will rid you out of their bondage, and I will redeem you with an outstretched arm, and with great judgments.
  4. Deuteronomy 7:19 the great trials which your eyes saw, the signs, the wonders, the mighty hand, and the outstretched arm, by which Yahweh your God brought you out. So shall Yahweh your God do to all the peoples of whom you are afraid.
  5. Deuteronomy 7:8 but because Yahweh loves you, and because he desires to keep the oath which he swore to your fathers, Yahweh has brought you out with a mighty hand and redeemed you out of the house of bondage, from the hand of Pharaoh king of Egypt.
Hebrews 8:13 WEB
In that he says, "A new covenant", he has made the first obsolete. But that which is becoming obsolete and grows aged is near to vanishing away.
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Greek Nestle 1904

ἐν τῷ λέγειν Καινὴν πεπαλαίωκεν τὴν πρώτην· τὸ δὲ παλαιούμενον καὶ γηράσκον ἐγγὺς ἀφανισμοῦ.

  • ἐν ἐν preposition G1722
  • τῷ article · dative singular neuter G3588
  • λέγειν λέγω verb · present active infinitive G3004
  • Καινὴν καινός adjective · accusative singular feminine G2537
  • πεπαλαίωκεν παλαιόω verb · perfect active indicative, 3rd person singular G3822
  • τὴν article · accusative singular feminine G3588
  • πρώτην· πρῶτος adjective · accusative singular feminine G4413
  • τὸ article · nominative singular neuter G3588
  • δὲ δέ conjunction G1161
  • παλαιούμενον παλαιόω verb · present middle or passive participle, nominative singular neuter G3822
  • καὶ καί conjunction G2532
  • γηράσκον γηράσκω verb · present active participle, nominative singular neuter G1095

Punctuation is editorial — the manuscripts carry none.

See also 5
  1. 2 Corinthians 5:17 Therefore if anyone is in Christ, he is a new creation. The old things have passed away. Behold, all things have become new.
  2. Hebrews 7:18 For there is an annulling of a foregoing commandment because of its weakness and uselessness
  3. Hebrews 7:11 Now if perfection was through the Levitical priesthood (for under it the people have received the law), what further need was there for another priest to arise after the order of Melchizedek, and not be called after the order of Aaron?
  4. Hebrews 9:15 For this reason he is the mediator of a new covenant, since a death has occurred for the redemption of the transgressions that were under the first covenant, that those who have been called may receive the promise of the eternal inheritance.
  5. Hebrews 9:9 This is a symbol of the present age, where gifts and sacrifices are offered that are incapable, concerning the conscience, of making the worshiper perfect,
Jeremiah 2:11 WEB
Has a nation changed its gods, which really are no gods? But my people have changed their glory for that which doesn't profit.
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  1. Romans 1:23 and traded the glory of the incorruptible God for the likeness of an image of corruptible man, and of birds, four-footed animals, and creeping things.
  2. Isaiah 37:19 and have cast their gods into the fire; for they were no gods, but the work of men's hands, wood and stone; therefore they have destroyed them.
  3. Psalm 106:20 Thus they exchanged their glory for an image of a bull that eats grass.
  4. Jeremiah 16:20 Should a man make to himself gods which yet are no gods?"
  5. Micah 4:5 Indeed all the nations may walk in the name of their gods, but we will walk in the name of Yahweh our God forever and ever.
Exodus 4:5 WEB
"This is so that they may believe that Yahweh, the God of their fathers, the God of Abraham, the God of Isaac, and the God of Jacob, has appeared to you."
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See also 5
  1. Exodus 19:9 Yahweh said to Moses, "Behold, I come to you in a thick cloud, that the people may hear when I speak with you, and may also believe you forever." Moses told the words of the people to Yahweh.
  2. Genesis 26:2 Yahweh appeared to him, and said, "Don't go down into Egypt. Live in the land I will tell you about.
  3. Exodus 3:15 God said moreover to Moses, "You shall tell the children of Israel this, 'Yahweh, the God of your fathers, the God of Abraham, the God of Isaac, and the God of Jacob, has sent me to you.' This is my name forever, and this is my memorial to all generations.
  4. Genesis 48:3 Jacob said to Joseph, "God Almighty appeared to me at Luz in the land of Canaan, and blessed me,
  5. Genesis 18:1 Yahweh appeared to him by the oaks of Mamre, as he sat in the tent door in the heat of the day.
Nehemiah 9:32 WEB
Now therefore, our God, the great, the mighty, and the awesome God, who keeps covenant and loving kindness, don't let all the travail seem little before you that has come on us, on our kings, on our princes, on our priests, on our prophets, on our fathers, and on all your people, since the time of the kings of Assyria to this day.
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See also 5
  1. Deuteronomy 7:9 Know therefore that Yahweh your God himself is God, the faithful God, who keeps covenant and loving kindness to a thousand generations with those who love him and keep his commandments,
  2. Nehemiah 1:5 and said, "I beg you, Yahweh, the God of heaven, the great and awesome God who keeps covenant and loving kindness with those who love him and keep his commandments,
  3. Daniel 9:8 Lord, to us belongs confusion of face, to our kings, to our princes, and to our fathers, because we have sinned against you.
  4. Daniel 9:4 I prayed to Yahweh my God, and made confession, and said, "Oh, Lord, the great and dreadful God, who keeps covenant and loving kindness with those who love him and keep his commandments,
  5. Micah 7:18 Who is a God like you, who pardons iniquity, and passes over the disobedience of the remnant of his heritage? He doesn't retain his anger forever, because he delights in loving kindness.

From the interpretive tradition

Our old history ends with the cross; our new history begins with the resurrection.
Watchman Nee The Normal Christian Life, ch. 3 pastor · chinese house church
This is truly the vision of God: never to be satisfied in the desire to see Him.
Gregory of Nyssa Life of Moses, II.239 father · eastern public domain
The great redemptive religion which has always been known as Christianity is battling against a totally diverse type of religious belief, which is only the more destructive of the Christian faith because it makes use of traditional Christian terminology.
J. Gresham Machen Christianity and Liberalism, ch. 1 theologian · reformed public domain

A worked example. Ask your own and it starts a new thread.