Did God change from the Old Testament to the New? Was God more violent and harsh in the Old Testament than in the New?
Sometimes, people have difficulty reading the Old Testament because there is so much violence. They might read how God commanded Israel to completely annihilate the pagan nations that were living in the Promised Land which was given to Israel. For example, 1 Samuel 15:3 says, “Now go and strike Amalek and devote to destruction all that they have. Do not spare them, but kill both man and woman, child and infant, ox and sheep, camel and donkey.” This sounds terribly cruel, so why would God want the entire nation destroyed, including women, children, and infants? Sometimes, the Bible does not give us express reasons for God’s action, but we must trust God for He always acts righteously and always does good.
Just because we don’t understand why God does certain things, even things that appear cruel to us, doesn’t mean it’s wrong. If we do not understand the “Why,” then we must trust the Who, and that is God Who must have good reasons. That’s enough for me. For one thing, God did not want these pagan nations surviving. If some of them were left alive, in time, they would grow, and they would have influenced Israel into falling into idolatry. The Amalekites lived in the land called Moab, and we know that the Moabites pagan religion was as evil as it gets. They sacrificed their own children in the fire, and later, they influenced some of the kings of Israel to do the very same detestable practices. God wanted these child-sacrificer’s gone! Maybe the reason there had to be such a total destruction of these pagan nations was because God did not want them remaining in the land. Eventually, some of these nations did influence Israel, and predictably, they fell into idolatry.
Those who believe that God is kinder and gentler in the New Testament than in the Old Testament, should read the Book of Revelation, and read some of Jesus warnings about the coming judgment of God (Rev 20:12-15). Jesus words must have burned the ears of the self-righteous, religious leaders, because He told them “You serpents, you brood of vipers, how are you to escape being sentenced to hell” (Matt 23:33)? The Apostle John writes that “if anyone’s name was not found written in the book of life, he was thrown into the lake of fire” (Rev 20:15), so you still think God is more loving in the New Testament than in the Old? John writes that “the cowardly, the faithless, the detestable, as for murderers, the sexually immoral, sorcerers, idolaters, and all liars, their portion will be in the lake that burns with fire and sulfur, which is the second death” (Rev 21:8). If there is a difference in the level of violence, it may actually be higher in the New Testament that the Old, because the judgment of God and comes with no end. At least a physical death was over quickly in the Old Testament.
I Change Not
God is not like a man. He cannot lie. He cannot change either. God does not change, and for that we should be thankful. Imagine if God changed His mind about us, and thought, “I see Jack’s really messing up down there…I don’t think I’ll save him after all.” Of course, there is no hint that God does that. Jesus says whoever believes in Him has eternal life, and that is in the present tense, meaning we already have eternal life. If we lost it, then it wasn’t eternal after all, but God thunders from heaven, “For I the LORD do not change; therefore you, O children of Jacob, are not consumed” (Mal 3:6). God says I do not change, so Jacob (or Israel) will not be forsaken and consumed. God is not going to change His mind about Israel’s future. God is therefore, the same in the Old Testament as in the New Testament. The covenants have changed, but not God. Jesus Christ is God, and so we can also say “Jesus Christ is the same yesterday and today and forever” (Heb 13:8).
Jesus Changes Not
Jesus does not change because He is God, and God does not change. It is our own perception of reading the Bible that we think God has changed from the Old Testament to the New. God has no need of change like we do. He is completely and perfectly holy and sinless; He is omniscient (all-knowing), omnipresent (present, everywhere, always), and omnipotent (all-powerful), so how could He improve on that? You cannot improve on perfection, and He is perfect in every way. God is the very same God in the Old Testament as He is in the New Testament. The way God approaches people is different, and for a time, God required animal sacrifices to cover sin, but they really never took them away because the sins kept coming back. Then, Jesus “entered once for all into the holy places, not by means of the blood of goats and calves but by means of his own blood, thus securing an eternal redemption” (Heb 9:12). That’s a change…but it’s not God Who changed. If anything is new, it’s the New Covenant through Jesus Christ.
It may appear that God was harsher or more violent in the Old Testament than in the New, but God Himself has not changed…and never will…for billions and billions of years, and if God saw fit to have the pagan nations around Israel destroyed completely, man, woman, and child, then we should not try to make judgments about His decisions. He is God. His ways are not our ways…His thinking is superior to our thinking. He sees everything and all the implications…we see only what’s in front of our face. God says only I can declare “the end from the beginning and from ancient times things not yet done, saying, ‘My counsel shall stand, and I will accomplish all my purpose” (Isaiah 46:10). Who are we to question God, because “The LORD of hosts has sworn: “As I have planned, so shall it be, and as I have purposed, so shall it stand” (Isaiah 14:24). By the way, His plan is infinitely better than ours.
Here is some related reading for you: Is Increasing Violence a Sign of the End Times? 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible: English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.