"I like the New Testament. The Old Testament seems so mean. I want the God of love not the God of anger."
In my four years in full time ministry, I have heard this or something like this from dozens of people. The Old Testament is different from the New Testament, this is true. One is written in Koiné Greek (or common Greek), the other in Ancient Hebrew. Greek is a very noun-centric language, Hebrew a very verb-centric language. But does the Old Testament describe a different God than the New Testament?
From the earliest days of Christianity, people have made this claim again and again, the most famous being the followers of Marcion. Marcionites believed that the God of the Old Testament was fundamentally different from Jesus and Jesus came to defeat the OT God.
What Marcion and the Marcionites had to do was cut out significant passages of the NT in order to make this work. Jesus says repeatedly that I am the Alpha and Omega, I and the Father are One, the God of Abraham, Isaac, and Jacob, etc.. Jesus quotes texts from the Old Testament unceasingly.
Marcionitism is, in fact, a heresy. A heresy is not something bad or wicked in and of itself but a willful distortion of revealed Truth about who God is. Marcion couldn't stomach that the God of the Jews was the God of Jesus and so he said that he was not.
But what does that leave us with the earnest confusion around the God of the book of Joshua (with all of its violence) and the God of Jesus Christ (with all of his talk of love) being one and the same? People are not foolish or heretical to have discomfort in reading of wrath.
On one level, we should remember that there are a number of wrath passages in the New Testament. In Matthew 25, probably the most famous text used to describe social justice, the last half includes a lot of wrath.
“Then he will say to those on his left, ‘Get away from me, you who will receive terrible things. Go into the unending fire that has been prepared for the devil and his angels. I was hungry and you didn’t give me food to eat. I was thirsty and you didn’t give me anything to drink. I was a stranger and you didn’t welcome me. I was naked and you didn’t give me clothes to wear. I was sick and in prison, and you didn’t visit me.’ - Matthew 25:41-43
As well, the Old Testament is full of love and grace and mercy. For example, from Isaiah 30
Nonetheless, the Lord is waiting to be merciful to you,
and will rise up to show you compassion.
The Lord is a God of justice;
happy are all who wait for him. - Isaiah 30:18
The Old Testament is called the Old Testament because it testifies to God in a prior way, not an outdated way. As Jesus says, 'I did not come to replace the law but to complete it.' We believe that the God of Abraham, Isaac, and Jacob is the God revealed in Jesus Christ by faith. This is where the Article of Religion comes in because the articles describe claims about God that have already been revealed. Claims that we need not re-litigate it again and again but can search to see how they are true.
Jesus does not replace the law but fulfills it. Jesus does not replace God's covenant with Israel but completes it and draws all people into that special relationship with God. This is good news.
Article VI — Of the Old Testament
The Old Testament is not contrary to the New; for both in the Old and New Testament everlasting life is offered to mankind by Christ, who is the only Mediator between God and man, being both God and Man. Wherefore they are not to be heard who feign that the old fathers did look only for transitory promises. Although the law given from God by Moses as touching ceremonies and rites doth not bind Christians, nor ought the civil precepts thereof of necessity be received in any commonwealth; yet notwithstanding, no Christian whatsoever is free from the obedience of the commandments which are called moral.