Didn’t Jesus come to show us the Old Testament God was not the God of love? Isn’t the God of Moses a God of rules and fear and the God of Jesus a God of life and joy?
Absolutely not. The idea espoused here is not one found on the lips of Jesus or his apostles, but upon the lips of the anti-Semite Marcion, who lived in the second century. It is a grotesque misreading of the New Testament to claim that Jesus repudiated the revelation given to Moses. As Jesus himself says, “Think not that I have come to abolish the Law and the prophets; I have not come to abolish them but to fulfill them” (Mt 5:17).
The Church emphasizes the continuity between how God revealed himself to our elder brothers, the Jews, and how he revealed himself at the beginning of the Christian age-first because it is a fact and second because viewing Old Testament revelation as somehow opposed to Christianity can lead to tragic and sinful persecution of the Jews, as history has borne tragic witness. There is no opposition between the character of God in the Old Testament and in the New. In the Old Testament we are told to “give thanks to the Lord, for he is good, for his steadfast love endures for ever” (Ps 136:1), while in the New Testament Jesus commands us to fear God (Lk 12:5).
It is profoundly unjust to both Judaism and Christianity to talk about the Old Covenant as a religion of “rules and fear” and of the New Covenant as simply sweetness and light. Judaism is full of a warm celebration of life and joy and Christianity is quite capable of stressing the towering majesty and even terror of God. Read the book of Revelation or the book of Hebrews or Jesus’ words to the hypocrites of his day (Mt 23) if you don’t believe this.