Q: Why were the laws of Moses (ie “eye for eye, and tooth for tooth”) so harsh compared to Jesus' teaching of forgiveness?

Biblical scholars tell us that as Christians we have to read the Old Testament with the New Testament in mind, that the New Testament is the culmination of God's saving work begun in the Old Testament. Thus we will see that the laws of Moses were fulfilled “by” Jesus and “in” Jesus:

In Matthew 5, Jesus redefined murder (21-26), adultery (27-30), divorce (31-32), oaths (33-37), eye for an eye (38-42), love the enemies (43-48).

Here are Jesus words redefining ‘eye for an eye’: “You have heard that it was said, ‘Eye for eye, and tooth for tooth.’ (Ex.21:24, Deut.19:21, Lev.24:20). But I tell you, do not resist an evil person. If someone strikes you on the right cheek, turn to him the other also. And if someone wants to sue you and take your tunic, let him have your cloak as well. If someone forces you to go one mile, go with him two miles. Give to the one who asks you, and do not turn away from the one who wants to borrow from you.”

Jesus Christ is the “end of the Law”. This is what St Paul tells the Romans: “Christ is the end of the law so that there may be righteousness for everyone who believes”. (Rom.10:4).

Since Jesus Christ fulfills the Law by His person and work, believers are under a new law; the obligation to walk by the Spirit of life through faith (Rom. 8:2-4). If we are led by the Spirit, then we are not under the Law (Gal. 5:18). Again St Paul says “For sin shall not be your master, because you are not under law, but under grace”. (Rom.6:14).

Jesus has not violated the Law nor even ignored it; He has fulfilled it.