It is common for new testament believers in Jesus Christ to hold a muddled view of the "old testament God." Was God full of grace before the incarnation? Was God less loving and more harsh before the advent of the Messiah? Was God all "law" in the OT and only warm fuzzy grace in the NT?
While it is true that history is a story of God's self-revelation and we have most graciously and clearly seen the radiance of God's glory in Christ Jesus, God is consistent and was compassionate and gracious before the incarnation.
I like what Hill & Walton say in their Survey of the Old Testament on their discussion of Deuteronomy:
"We are used to drawing a sharp contast between law and grace. This would have puzzled the ancient Israelite for whom there was hardly any greater display of God's grace than that demonstrated in his giving of the law. In the ancient Near East, gods were not known for their consistency. Worshipers were left to guess what might please their god or displease him, and this could change rom day to day. That doubt nd uncertainty led to constant confusion, and one could only guess whether he or she was in favor or out of favor by evaluating one's daily fortunte. The law changed all that for the Israelites. Their God had chosen to reveal himself and to tell them plainly what he expected of them...there are striking constrasts between [the laws in the Bible and the ancient Near East]...One result of this perspective is that in the Old Testament the Israelites are not heard complaing about the burdensomness of the law. It was a great example of God's love for them...the law was viewed as a delight rather than drudgery, as freedom of revelation rather than fetters of restriction."
When Moses asked to see God's glory, Yahweh agreed, albeit he couldn't do so face to face or else Moses would have melted in the radiance of God's majesty. But he did reveal his glory - with words: "The LORD, the LORD, the gracious and compassionate God, slow to anger and abounding in love and faithfulness, maintaining love to thousands of generations, and forgiving wickedness, rebellion and sin. Yet he does not leave the guilty unpunished; he punishes the children and their children for the sin of the fathers to the third and fourth generation."