Regarding the matter of incest, I would like to share my personal reflections.
What is the most important thing in a human person? It is the spirit or we called, our human soul, the breath of God that makes us a living human being. That is why Jesus tells us in the Gospel tells us that it is better for a person to go to heaven without an eye or without a limb than a complete and whole body but ends itself in eternal punishment.
For the love of His Son, Jesus, God created us, human beings in His Image and likeness, body from the soil of the earth, but the soul, from the very Breath of God. It is also part of His Divine Plan that He created the whole universe, and specially, human beings, that they should propagate, fill the earth and subdue it and one day return back to Him in our heavenly home. That was His Master Plan. They are just fulfilling God’s command and orders, His Will, and for His chosen people, the Israelites, there is nothing wrong about it.
Remember Jesus teachings, it is the spirit that gives life, the body has nothing to do with it. It is our soul that God is more interested about. Our bodies are just temporally instrument or vehicle for our soul to be present in this material world and to do things which only with a human body, we are able to do. But, still, our spirit should be the master of our body.
Our first parents, and those in the earlier times are just following God’s orders or will, to multiply, fill the earth and subdue it. They just obey God’s Will, God’s Word, in living out thier everyday lives, thier daily simple lives.
Then at another stage of human history, when God said, there shall be no more marriages of close relatives, and if you do so you will be commiting the sin of incest. That is His Law, His Command, His Word, and when His Word is spoken we are to obey it.
Just like a countries Legislation Law, if a certain issue or law is enforce by the goverment, the next time you commit it will be considered an offence, a crime and will have to face the consequence of it. So it is with God’s Law, His Commands.
I believe that in everything, God knows the best, He sees through our future, our lives and even the future of our whole planet. At the appopriate time He will do what is neccesary, even if our bodies should get hurt, that our souls may be at peace and salvation.