Many laws of the Old Testament are contrary to the law that Jesus taught us in the Gospel because do not contemplate the mercy and forgiveness. Therefore, they are an unbearable burden. Here are some of these Old Testament laws:
"And if a man take a wife and her mother, it is infamy: they shall burn him and them with fire, that there be no infamy among you". (Leviticus 20:14)
"And the daughter of any priest, if she profane herself by playing the whore, she profaneth her father: she shall be burned with fire". (Leviticus 21:9)
"And if a man cause a blemish in his neighbour, as he hath done, so shall it be done to him; breach for breach, eye for eye, tooth for tooth: as he hath caused a blemish in a man, so shall it be done to him". (Leviticus 24:19-20)
" If a man have an unmanageable and rebellious son, who hearkeneth not unto the voice of his father, nor unto the voice of his mother, and they have chastened him, but he hearkeneth not unto them; then shall his father and his mother lay hold on him, and bring him out unto the elders of his city, and unto the gate of his place; and they shall say unto the elders of his city, This our son is unmanageable and rebellious, he hearkeneth not unto our voice; he is a profligate and a drunkard. And all the men of his city shall stone him with stones, that he die. And thou shalt put evil away from thy midst; and all Israel shall hear and fear". (Deuteronomy 21:18-21)
" When men fight together one with another, and the wife of the one come near to rescue her husband out of the hand of him that smiteth him, and stretch out her hand, and seize him by his secret parts, thou shalt cut off her hand; thine eye shall not spare". (Deuteronomy 25:11-12)
All these laws are contrary to the law that Jesus taught us in the Gospel, which command forgive, not to hurt anyone, no kill. Jesus Christ command us to have mercy. So, Jesus Christ, with His teaching of the Gospel (love, mercy and forgiveness), abolished all those cruel laws Old Testament, because they were not God's Law.