I dare say, it seems to me that most people, Christians included, view the God of the Old Testament as a pretty loathesome fellow. Some would never admit this, but let's face it...most of the time we view His treatment of people in the Old Testament, and even His own chosen people, as impatient, inflexible...and even perhaps inconsistent, or moody. For what it's worth, I do not think it is fair or accurate to view the God of the Old Testament as being different than the loving Father God as revealed by Jesus in the New Testament. He is, indeed, one and the same. Here are a couple of thoughts for your consideration.
Allow me to reintroduce you to the Prophets - the Old Testament harbingers of doom, gloom, impending judgment and just plain dourness. We will start with Jonah, who just so happens to be one of my favorites. And yes, you might have guessed he would be one of my obvious picks. After all, God basically forced him to go call the people of Ninevah to repentance. The people of Ninevah...also known as the Assyrians...are the same people who, a few decades after their repentant response to Jonah's message, would take Israel into harsh captivity for 70 years. God, in fact, knew this, for He had been warning His people through the prophets for a very long time that it was coming! Yet He inarguably went out of His way to show astounding mercy and great concern for these people who were known by all the world for their cruel and barbaric ways. In fact, His response to Jonah's complaints in Jonah 4:11 sounds almost as if it comes from a loving and concerned Father who knows His children (in this case the Ninevites) cannot survive without His care.
A second (again, often-cited) prophetic voice of the compassionate, loving God of the Old Testament is Hosea. Those people who say that the God-as-Lawgiver/God-as-Meter-Out-of-Justice picture of the Old Testament is out of character with the paternal God of the New, seem to overlook the fact that the God of Hosea is completely out of character with the God who ordered Israel to abstain from intermarriage with pagans, as well as sexual immorality of any kind. He actually instructed Hosea to marry a prostitute! And this was not a marriage for the sake of conversion...Gomer (the prostitute Hosea married) did not turn from her promiscuous ways. Yet every time she wandered, Hosea went and bought (as in, with money) her back and loved her. And this unrelenting, all-forgiving love of the woman who seems to have wanted not much if anything to do with him, is compared with God's love for His people. My point in highlighting this seemingly inconsistent view of God in the Old Testament is to emphasize that God has always been beyond our comprehension - we have never been able to peg Him down and hold Him in some kind of neat "box" of our own theological understanding.
And then we have the prophets (like Isaiah) who continually warned the people to repent of their sin and rejection of God, or else face estrangement from Him and captivity to other, much crueller, earthly masters. Wait - that doesn't sound very gracious, does it? In fact, it sounds rather punitive and vengeful and maybe even bitter. Admittedly, God even refers to Himself several times as being downright jealous. But I am not sure the prophets were warning the people that they were going to be "punished" per se. They were warning the people that they were going to suffer. One might ask if there is a difference. I believe there is.
Suffering does have a purging effect. However, the kind of suffering that is the result of poor choices does not erase whatever transgression was done to bring it about. So how can it be effective as punishment? Suffering, while horrible in most of our thinking, and to be avoided at all cost, has great value. It reminds us who we are, what we lack...what we need and cannot provide for ourselves. Throughout the Prophets, while they warn of impending suffering, they continually call the people to repent and turn back to God, who is waiting with open arms to be their Father, their Provider, their All-in-All. He pleads with them to reconsider their ways (Habakkuk). He reassures them that no matter what, even if they don't repent and choose rather to face great suffering, His invitation will be waiting for them on the other side...His ancient promises will still be there, intact, ever progressing toward fulfillment. He will remain theirs, faithfully, just waiting for them to allow Him to provide them with the loving relationship He has offered all along.
The Old Testament Law itself can be looked at in the same way - a tool of suffering (Galatians refers to it as a schoolteacher) to remind rebellious and obstinate humanity that they cannot provide what they need, neither temporally nor eternally, for themselves. They need Someone greater to do it for them. And all along, Someone greater waits to do just that.
The God of the Old Testament...the God who grieved over the ruin of His original plans for humanity (Genesis 6:6)...the God who promised to redeem the perfect relationship humans had willingly shattered (Genesis 3:15; 12:3, etc.)...the God who valued love above all else (Deuteronomy 6:5; Leviticus 19:18)...has been the same since the very beginning. He has never changed.
Followers of Jesus do not serve a different God than the One revealed in the Old Testament. He has never been a God of hatred and wrath and fear, but a God of love and restoration and hope.