Exodus Chapters 12-30

While reading chapter 21 of Exodus, God was giving Moses some of the basic rules he wanted humans to follow. In verses 22-25 he starts to say that an eye shall be paid with an eye, an arm with an arm, and so on. This left me confused because i always thought that the entire Catholic Religion was about learning to forgive others and repent on your mistakes, not take revenge. This also goes against Jesus's teachings, more specifically when he states that when somebody strikes you on your right cheek, you should offer your left cheek. It never says anything about striking the offensor back. Ghandi actually has a very famous quote which relates to this topic. He says that "An eye for an eye makes the whole world blind", which makes perfect sense. If everyone started taking revenge on whoever offended them, no one would be spared because we all have hurt someone in some point of our lives. Referring also to the rules, I thought that the statements were very similar to those established by Hammurabi in Ancient Mesopotamia. Finally, in Chapter 24, verse 18, Moses was sent up to the mountain to talk with God. He spent a total of forty days and forty nights, which is the exact length of the flood that had Noah building an ark. Why is this number repeated? Does it have any special significance? It doesn't appear to have one, but it has to have some kind of significance to be mentioned twice, but more importantly it was phrased in the exact same way. It would be interesting to know its actual relevance.