Galatians 3:23-25 But before faith came, we were kept under the law, shut up unto the faith which should afterwards be revealed. Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith. But after that faith is come, we are no longer under a schoolmaster.
James 2:10-11 “For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all. For he that said, Do not commit adultery, said also, Do not kill. Now if thou commit no adultery, yet if thou kill, thou art become a transgressor of the law.”
Galatians 3:10 "For as many as are of the works of the law are under the curse: for it is written, Cursed is every one that continueth not in all things which are written in the book of the law to do them."
God gave us the law to show us his moral standard. James 2:10-11 says, “For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all. For he that said, Do not commit adultery, said also, Do not kill. Now if thou commit no adultery, yet if thou kill, thou art become a transgressor of the law.” Romans 5:12 says, " Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:" Romans 6:26 says, “For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.“ God chose to set forth his Son to atone for our sins even though we deserve death according to the law.
Matthew 5:38 says, “Ye have heard that it hath been said, An eye for an eye, and a tooth for a tooth:” This was said in Exodus 21:24, Leviticus 24:20, and Deuteronomy 19:21. Jesus goes on to say in Matthew 5:39, “But I say unto you, That ye resist not evil: but whosoever shall smite thee on thy right cheek, turn to him the other also.”
Jesus is not changing the law. Measure for measure is still God's moral standard. Jesus, however, is teaching the gospel of grace. Matthew 5:17 says, “Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil.” We deserve death and Jesus came that we might have life and have it more abundantly.
Matthew 5:43-45 says, “Ye have heard that it hath been said, Thou shalt love thy neighbour, and hate thine enemy. But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you; That ye may be the children of your Father which is in heaven: for he maketh his sun to rise on the evil and on the good, and sendeth rain on the just and on the unjust.”
Matthew 5:14-15 says, “For if ye forgive men their trespasses, your heavenly Father will also forgive you: But if ye forgive not men their trespasses, neither will your Father forgive your trespasses.”
There is a parable that Jesus told to illustrate this. A lord forgave his servant a large debt and that same servant didn’t act in the same mercy. We see in Matthew 18:32-35, “Then his lord, after that he had called him, said unto him, O thou wicked servant, I forgave thee all that debt, because thou desiredst me: Shouldest not thou also have had compassion on thy fellowservant, even as I had pity on thee? And his lord was wroth, and delivered him to the tormentors, till he should pay all that was due unto him. So likewise shall my heavenly Father do also unto you, if ye from your hearts forgive not every one his brother their trespasses.”
The law is our God’s moral standard. The gospel is our God’s gift of undeserved grace. The law tells us that we do not live up to his standard and are dead in sin. The gospel tells us in John 1:12-13, “But as many as received him, to them gave he power become the sons of God, even to them that believe on his name: Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.” Those who God has called to faith have been forgiven must offer the same forgiveness to all.
PS If you read all of the laws concerning slaves, you would see that they had plenty of rights and were not at all allowed to be treated like the Americans treated slaves.