Recently someone put this argument to me, though it was not the first time I have heard it:
The Bible seems to shift between how it presents God: in the Old Testament he comes across as a God of judgement, vengeance, fire and brimstone; while in the New Testament he seems to be the other extreme, of kindness, love and peace.
Then they went on to say:
It's all about control: the people who invented Judaism in the Old Testament times lived in a harsher, less civilised world and their God fitted in with that so that the people could be controlled by the religion. In New Testament times, the Romans introduced a more civilised way and the religious people changed the idea of God to fit with the times in order to control the people.
Interesting idea, on the surface, but a complete reading of the scriptures soon proves this idea unfounded. Unsurprisingly many people have this misconception about God's nature. I guess if you've only been to a handful of church services, if you listen to the media's portrayal of God and if you have seldom read the Bible, how could you think otherwise?
The Bible teaches us that God is consistent in character throughout: he does not change. Malachi 3:6 states "For I the LORD do not change", and if you wanted a New Testament verse (though the whole Bible is God's word), then read Hebrews 13:8 "Jesus Christ is the same yesterday and today and forever."
Now I'm sure many could quote passages from the Old Testament about God in judgement, as well as quoting from the New Testament that God is a God of love (of course God is both of these things, but he is not solely one in the Old and another in the New), but here are some scriptures which demonstrate that, on top of this, God is loving in the Old and of judgment in the New.
Firstly consider the Old Testament scriptures: in Genesis 1:28, as soon as God has made man, and before he does anything else to them, he blesses them, demonstrating his kindness from the offset. How about Exodus 34:6 "The LORD passed before him [Moses] and proclaimed, "The LORD, the LORD, a God merciful and gracious, slow to anger, and abounding in steadfast love and faithfulness, keeping steadfast love for thousands, forgiving iniquity and transgression and sin, but who will by no means clear the guilty, visiting the iniquity of the fathers on the children and the children’s children, to the third and the fourth generation.", which actually portrays God as both judging and loving. Psalm 100:5 "For the LORD is good; his steadfast love endures forever, and his faithfulness to all generations." Read Psalm 136, the whole of it, because every other line is "His steadfast love endures forever", how could a people not loved, but only judged, by God write something like this? There are many more such passages.
Secondly, let us deal with the New Testament. God's love is so evident here, but he also casts judgement as required. In Luke 11:37-52, Jesus gives a blistering rebuke to the religious people of the time. Consider Luke 19:27, a verse at the end of a parable which tells of a nobleman (symbolic for God) entrusting his servants to invest his riches, stating "But as for these enemies of mine, who did not want me to reign over them, bring them here and slaughter them before me." Acts 5:1-12 tells the story of Ananias and Sapphira who collapsed dead after lying to the Holy Spirit. 2 Timothy 4:1 describes Jesus as judge, as does 1 Peter 4:5. Finally the book of Revelation is filled with passages of the coming judgement of Christ as he returns, such as Revelation 6, 14:14-20 and chapter 16, to name a few. A brief aside, notice how John sees Jesus in Revelation 1: 14-16, a God of true matchless awesomeness, not Jesus meet and mild, "The hairs of his head were white, like white wool, like snow. His eyes were like a flame of fire, his feet were like burnished bronze, refined in a furnace, and his voice was like the roar of many waters. In his right hand he held seven stars, from his mouth came a sharp two-edged sword, and his face was like the sun shining in full strength." Again, these are but a taste: search the scriptures which are full of such examples.
In response to the idea that religious people changed the idea of God to suit the times, let me say that God is not an idea that is modified. God revealed himself to us through Jesus (see Hebrews 1:1-3) and the people who wrote about Jesus were his first disciples such as Peter, John, James who wrote books in the New Testament about Jesus and how he had revealed himself to them. Paul, who met Jesus after his ascension on the road to Damascus in Acts 9, wrote much of the New Testament. Most of Jesus' first disciples, and Paul were put to death for preaching Christ. Clement, an early Church father, wrote to the church in Corinth about Peter's death at the hands of Emperor Nero; traditionally, it is believed that Peter was crucified upside down. The point is this: Jesus followers in the First century had the choice to abandon their faith in him, or, in many cases, die an unpleasant death: they chose the latter. If they made it up (remember, they were the ones who wrote about him) why would they die for what they knew to be a lie? Of course they didn't die for a lie, because it isn't a lie, but the truth of God.
I leave you with a quote from the song Creed by the Christian band, Third Day.
I did not make it, no it is making me
It is the very truth of God and not the invention of any man