Christ told us they were the same, although it wasn’t until Paul was assigned as the gentile apostle that God was accepted as God of all men.
Today many think the OT did not portray God accurately but Christ changed God. They use the word fulfilled to justify that. I believe the word fulfilled in bible meaning tells us that Christ was from the beginning, Christ was explained all through the OT, and Christ as He acted in our kind of time did, or fulfilled, all that was told of Him.
An example of the change often taught was grace as of the NT, law of the OT. Yet even Abraham shows us God's grace, as Abraham's faith was accounted as righteousness. The blessings given at the covenant at Mt. Sinai never included salvation, that was only by grace.
There was a group of people told of in Acts who believed God was eternal, the same always. They believed as I do that the OT often gives us a more complete picture of what the NT teaches, but there is never a disagreement between the two.
Acts 17: 11 the Bereans were more noble-minded than the Thessalonians, for they received the message with great eagerness and examined the Scriptures every day to see if these teachings were true. 12As a result, many of them believed, along with quite a few prominent Greek women and men.…
The God of the Old Testament is the same as the God of the New Testament, and the God of the Jews is the God of the Gentiles whether Old Testament or New Testament.
The only difference is Israel had the advantage over the Gentiles for the word of God was given to them.
And God worked with Israel for she was His chosen nation, and the headquarters of the world, which is why a Gentile when saved is part of the commonwealth of Israel, and Jerusalem the mother of us all, and the new earth called the New Jerusalem, which the 12 tribes of Israel, and the 12 apostles of the Lamb are written in the New Jerusalem, and Jesus said salvation is of the Jews.
As far as judgment God would judge right on earth in the Old Testament, and would fight for Israel against her enemies, where in the New Testament God does not do that for we are under grace, but judgment is still against all people who reject the truth to be given in the future, and God will fight for Israel in the future, and it is going on now for God will still fight for Israel like He said like birds flying He will take back Jerusalem, which is fighter pilots, jets, in the 6th day war, 1967, when Israel won the war and took control of Jerusalem, but will fight for Israel against all her enemies in the future which is the whole world, for the whole earth shall be gathered together against her.
So as far as judgment it is upon all rebellious whether Old or New, but in the New we are under grace, but God still fights for Israel which will come out more and more as the time approaches to the battle of Armageddon.
And salvation was still offered to the Gentiles in the Old, and they could receive it, for God said to Israel to treat the stranger as one of her own, and if they took hold of God's covenant they too would have salvation, as well as any Gentile of the other nations if they took hold of that covenant, although it would be not heard of by many of the world.
But then the Bible says that creation testifies that there is a God who created all things, and of His attributes, which one of them is love, for He provided food, and the means to make clothing, and shelter, so the world is without excuse, which if the Gentile that knew not the word of God in the Old, and His covenant, salvation was still available to them if they believed in a higher power, and loved people to the best of their ability, for love is the fulfilling of the law, and asked God to forgive them if anything was amiss.
For we know of Noah before Israel came about, and of Job before Israel came about, and others before Israel came about that had salvation, and of king Nebuchadnezzar who acknowledged the God of Israel for He is the greatest God of all the gods, and proclaimed throughout his kingdom to acknowledge the God of Israel, and if anyone said anything against Him they would be cut in pieces, and their house made a dunghill, which is why Babylon during his reign is referred to as gold, and rode on eagle's wings, and the best Gentile kingdom on earth at any time period, but when the king died the son blew it, and the kingdom was stripped from them and given to the Medes and Persians.
Had Babylon kept acknowledging the God of Israel she would still be the operating kingdom today.
So Gentiles could have salvation in the Old the same as the Jew, and many acknowledged the God of Israel, although the Jew had the advantage over them, and many did not know of her covenant, but by creation, and their conscience, could be right with God to be saved.
I do not look at a difference of God between the Old and New for salvation was still given to all whether Jew or Gentile, and God will judge all rebellious people who do not accept the truth whether Old or New, but it was on earth in the Old, where it is postponed because we are under grace, but judgment is still coming upon them.
But in the Old God speaks of His mercy endures forever, and His everlasting love for people, and He is tender hearted, and cares for people, and does not take pleasure in the death of the wicked, and His love for people, the same as the New.
There is no difference for His love was for all, and the same love whether Old and New, but Jesus brought it out for spiritual salvation to have a spiritual relationship with God opposed to a physical covenant with Him, but that love was the same in the Old.
I do not look at God any different whether Old or New, and His love the same whether Old or New, and salvation for Jew and Gentile whether Old or New, but in the Old it was physical blessings, where in the New Testament it is spiritual blessings.
Jesus did not bring out a new God for He has always been love whether Jew or Gentile, and the same love, but Jesus brought out that this God of love that has been in the Old Testament is now offering spiritual salvation instead of physical salvation, spiritual blessings instead of physical blessings, and eternal life prosperity in heaven, instead of prosperity on earth.
For God said I am the LORD, I change not, and Jesus is the same today, yesterday, and forever.
Why would people think the God of the Old would be different, and work different in the Old, than in the New, for He is the same.
Just because God judged on earth, and fought for Israel in the Old, does not mean He is different, for judgment is still upon all rebellious, and God fights for the saints but in a spiritual sense now to keep the enemy Satan away, and from spiritual deception, and will give them an escape from persecution like Jesus that would escape it for His time had not come yet, but God does not go against the heathen physically like in the Old, but they still will not escape judgment.
For whether judgment on earth for the Old, or judgment in the future for the New, they are still judged.
For that is the big reason people say that God behaves different in the Old than the New, for God judged on earth, and fought for Israel in the Old, but judgment is still upon the rebellious in the New, but we are under grace so God will not bring it out until the future.
But even in the Old Testament the Jews complained that those that did not love God prospered, and had no trouble, and their children had no trouble, because it was the same as the New, but God had to protect Israel for Jesus was coming through them so they would not be wiped out, and had to put down kingdoms when they spread their falsehood too far, and were cruel to hurt people.
And God said He winked at the ignorance of the heathen in the Old, but now commands them to repent, and for the most part left the Gentiles alone, unless they messed with Israel, or they were too cruel, and perverting the truth among the people where it had a big influence upon many people.
So God put down a 1000 to save 10,000, and if God had not intervened in the Old more people would of been hurt, and killed, and more people would of been void of the truth of God, and salvation.
So how is God a different God in the Old than in the New.
If a boy was walking in the park with his dad, and a man ran up with a knife to stab him, and his dad put him down, would the boy say, dad you are cruel, or would he thank his dad for saving his life.
So why would they think that God would be different in the Old when God only did it for the benefit of people, so less people would be physically hurt, or killed, and more people could see the truth of God, and His ways.
For they say He was a war monger in the Old, but they do not know the truth, for God did it for the people, and in the New God said, He does not correct us like fathers will correct their children for the pleasure of the parents, but He corrects us for our profit.
He was not a war monger in the Old but did it for the benefit of people, like He does it for the benefit of the people in the New.