So... this is my first time posting, and in fact, it was this specific thread that prompted me to join this site. I don't usually like to post, because most people- in my experience- refuse to accept anything other than what they already believe to begin with. But here goes...
Jesus did say that the Hebrews were given laws that were not in accordance with what God wanted, simply because their hearts were hard at the time. Matthew 19:7-8... "Why then," they(Pharisees) asked, "did Moses command that a man give his wife a certificate of divorce and send her away(for any and every reason)?" Jesus replied, "Moses permitted you to divorce your wives because your hearts were hard. But it was not this way form the beginning..."
It seems to be a very clear sentence to me. Were the Hebrews of those times capable of or willing to understand better? According to this, no, not at that time. I believe they also misunderstood things, as in the case of sacrifices...
Hosea 6:6 For I desire mercy, not sacrifice, and acknowledgment of God rather than burnt offerings.
Jesus reminded them often of this 'mercy, not sacrifice...'
And also, Isaiah 58:6-8 "Is not this the kind of fasting I have chosen: to loose the chains of injustice and untie the cords of the yoke, to set the oppressed free and break every yoke? Is it not to share your food with the hungry and to provide the poor wanderer with shelter-when you see the naked, to clothe him, and not to turn away from your own flesh and blood?"
The God of the OT is the same as the God of the NT. Only our understanding of Him has changed, or it should have, thanks to Jesus Christ.