Is the God of the Old Testament the same God?
Yes, and the church settled this in the second century when a man named Marcion argued otherwise and was thrown out for it. The simplest evidence is Jesus himself: he quotes the Old Testament constantly, calls its God his Father, and never once suggests he is dealing with a different or lesser being.
The instinct behind the question is understandable. The Old Testament has floods, plagues and armies; the New has a man telling people to love their enemies. Read the two quickly and they can seem to describe different beings.
Somebody argued exactly this very early, and what happened to him is instructive.
Marcion, and why he lost
Marcion of Sinope, in the second century, taught that the God of the Hebrew scriptures was a lesser deity — the creator of this messy material world, just but harsh — and that Jesus revealed a different, higher God of mercy who had nothing to do with him.
He was consistent about it. He produced his own Bible: no Old Testament at all, a trimmed version of Luke, and ten of Paul’s letters with the Jewish references removed.
Rome excommunicated him in 144. Tertullian, Justin Martyr and Irenaeus wrote against him at length, and the church’s answer was to affirm the whole of Scripture as one story with one God.
That is worth knowing because the question is not a modern discovery. It was put sharply, examined, and rejected while the ink was still fresh.
What Jesus does with the Old Testament
The most direct evidence is how Jesus treats those books.
He quotes them constantly — in argument, under temptation, and from the cross, where the words he cries out are from a psalm. He tells his opponents that the scriptures testify about him. He says he came not to abolish the law and the prophets but to fulfil them.
And the God he addresses as Father is unambiguously the God of Abraham, Isaac and Jacob. There is no moment where he distances himself from the God of Israel — a strange omission if he were revealing a different one.
Marcion had to cut the text to make his case. That is usually a sign about the case rather than the text.
The mercy is in the first half too
The contrast people carry does not survive reading either half properly.
The Old Testament’s own summary of God, given to Moses and repeated throughout, is that he is compassionate and gracious, slow to anger, abounding in steadfast love. Jonah is a book about a prophet furious that God forgave a foreign city. Hosea is a picture of God as a husband who will not stop pursuing an unfaithful wife.
Exodus 34:6KJVAnd the LORD passed by before him, and proclaimed, The LORD, The LORD God, merciful and gracious, longsuffering, and abundant in goodness and truth.And judgement is not absent from the New Testament. Jesus speaks about it more than anyone else in the Bible, and the last book is largely about it. If you are sorting by severity, the sorting does not fall where the objection assumes.
One story, or two
Underneath this is a question about what kind of thing the Bible is.
Christians read it as one story with a direction: a world made good, damaged, and being repaired, with the second half being the completion of the first rather than its correction. The pattern is set up early — a rescue from slavery, a lamb, a covenant — and Jesus keeps saying he is what those things were pointing at.
Cut the first half and the second stops making sense. The New Testament assumes the Old on nearly every page; take it away and you have a book about a Messiah with nothing for him to be the Messiah of.
Objections answered
But the tone is completely different.
The genres are different, which accounts for a lot: national history and law read unlike letters to small churches. And the two halves cover different situations — one is a nation with an army and a legal system, the other a persecuted minority with neither. The God described is the same; the circumstances are not.
Doesn't Jesus revise the law — 'you have heard it said, but I say'?
He intensifies it rather than replacing it: not only do not murder, do not hate; not only do not commit adultery, do not look at someone that way. That is tightening a standard, and in each case he is arguing against a lax interpretation rather than against the text.
Why does God seem to change his mind in the Old Testament?
The passages are usually about a stated intention conditional on behaviour, which changes when the behaviour does — Nineveh being the clearest case. And a God who never responded to repentance would be less good, not more consistent.
Shared ground, and where traditions differ
All Christians hold
Every tradition holds that there is one God, author of both Testaments, and all of them condemned Marcionism explicitly — one of the earliest matters the church settled together.
Related questions
Inspired by Got Questions — "What is Marcionism?". The argument is theirs; the words here are ours.
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