Many people have the idea that the God portrayed in the Old Testament is different than the one portrayed in the new. Upon a cursory look, this may seem plausible. In the old testament there are these humongous wars and judgements that are depicted, voluminous prophecies of downfall (Isaiah, I’m looking at you), and scores of the like material to be found. And of course we all know that the New Testament declares that God is love. Jesus bounces kids on his knees and teaches people to be good neighbors and love our enemies.
What this superficial analysis of the 2 cannons misses–besides the glaring cherry picking of the topics– is the simple temporal disanalogousness of the two collections of writings. What i mean is that even supposing a Young-Earth interpretation Genesis, the scope of the Old Testament is at least 4 thousand years. The new testament by contrast narrates at most 70 years. One might object that if you take in years covered by prophetic timelines, the NT then includes up until the Second Coming which at present is somewhere over 2010 years and counting. But then the Old Testament covers all that extra time also since Revelation quotes/paraphrases extensively from OT passages regarding the coming of Jehova to Israel, the judgement of the wicked and the exhaltation of the just so you don’t get any help there.
But aside from that, also in terms of the span of time it is authored in, yhere is a disparity. The OT was authored somewhere in the range of 1500 years (leaving aside the dating of and debate about the historicity of Job and also the undoubtedly oral history that finally gets at least compiled by Moses) whereas the NT is authored over somewhere around 55 years. So the NT is a collection which is authored in about 1/27th the time.
The OT has unbroken narrative covering the creation of the world unto the return from the Assyrian and Babylonian exiles. Again even assuming a Young-Earth interpretation, we have roughly 3500 years covered here. The NT narrates from a bit prior to the birth of Jesus until Paul’s transfer to Rome, thus around 60 years. So the NT chronicles around 1/60 ( 60/3500 ) of the time the OT does.
Any fair minded person should immediately realize that this throws the hypothesis under examination out the window. The OT should necessarily include more tradgedy and horror than the NT simply because it has room for it in a temporal sense. Consider just the tradgedy in the last 150 years with Stalin, Mao, Hitler, Pol Pot, WW1, WW2, Vietnam, disease, famine…
As far as the idea of God being inherently different in character in the testaments, consider two facts:
1) the mercy and grace of God was shown over and over throughout all of those extra years to Israel and other nations. God sends prophets to warn people to turn from wickedness and when they do He pardons and blesses them. E.g. Ninevah
2) Jesus warns that the temple will be destroyed and in AD 70 ish Jerusalem is beseiged, the temple burnt, and many slain. (Granted this part takes place after the narrative, but is alluded to by the NT narrative, and specifically by Mr. Kid bouncer neighbor lover).
Missing that God is one and the same is easy if you don’t think through the relevant facts or simply accept the rhetoric of some comparative religion professors and others who set forth the opposite idea. But once you actually look into it the idea that the testamentary accounts are disparate, you can see its so very implausible that it must be rejected.