A Sign of Promise
Genesis 9:13 (ESV) … “I have set my bow in the cloud, and it shall be a sign of the covenant between me and the earth.”
There are two different kinds of signs in the Bible. Some are miraculous, what the Bible speaks of as “signs and wonders.” There are whole clusters of these signs. Moses gave a series of such signs to Pharaoh. The miracles of Exodus, the plagues, were proof that God is truly God. In the New Testament we find the same thing during the earthly ministry of Jesus. The miracles were to show that Jesus was, as Nicodemus confessed, “a teacher who has come from God” (John 3:2). The other kind of biblical sign is not miraculous, at least not necessarily so. It is a symbol of spiritual truth. (Of course, these sometimes overlap. When the Lord Jesus Christ did certain miracles, such as the multiplying of the loaves and fish in Galilee and then spoke of himself as the bread of life, he was doing what was miraculous but at the same time was a symbol of the truth that he satisfies the needs of the human soul.)
Genesis 9:8–17 introduces us to the second kind of sign, the sign that is a symbol.
The rainbow was given to Noah following the flood, and the essential nature of this sign is that it is a thing of beauty. This is a case of the grace of God ministering to Noah after what must have been a most traumatic experience.
We speak of people being wounded by things that have come into their lives. Noah and those who were with him must have been wounded by the flood. They had not endured personal physical loss, but the civilization they had known was wiped out. The flood was a holocaust of major and unique proportions. It is difficult to see how they could have come through an experience like that without the wounds of the past on them. These wounds are the probable reason for the noticeable repetition as God gives the covenant. In the early chapters of Genesis the events more or less fly by. If we have any complaints about the early chapters of Genesis, humanly speaking, it is that God did not take time to tell us more.
We have all kinds of questions. By contrast, in the story of the flood we have great repetition. This one incident is expanded into several chapters, and when God gives the covenant he reiterates it again and again. In chapter 6 God says, “I’m going to establish a covenant.” In chapter 8 we get the covenant in detail. Then, at the beginning of chapter 9 God expands on it even more fully, saying, “I am never again going to destroy the earth by flood.” In the verses we are looking at now, God enacts the covenant and gives the sign of the rainbow.
Why this reiteration? It is not for the sake of God, who does not need to repeat things, but for the sake of Noah who needed to hear them. He needed to be reassured. He was wounded in soul. So God said again and again, “I am never again going to destroy the world by flood. You have seen the ugliness of sin and its effects, the horror of my judgment. I want to reassure you that I will not send a flood again, and in order to do that I am making a beautiful rainbow in the sky as the pledge of my promise.” As Noah looked at the rainbow he must have said, “Yes, that ministers to me. Because the God who is giving me this beautiful sign is not going to put us through such a judgment again.”
I do not know where you fall in that picture. But I know there are many people who carry the scars of the past within them. There is a book by William Styron entitled Sophie’s Choice. It tells the story of a young Jewish woman who survived one of the German death camps. She was confronted with a choice as she entered the camp. This choice is not talked about in the early pages of the book. It comes out only in the end. But when you get to it you know that it alone explains the agony of the earlier pages. As Sophie entered the death camp she had two children with her. One of the guards, apparently on a whim, told her she could keep one child but would have to let the other go off to the furnaces to die. This marred the mother irredeemably, and in the end she committed suicide because she was not able to cope with the past. There are people who have wounds like that—people who have suffered loss and tragedy.
To you I say, God is the God of beauty. God makes signs of beauty to say, “I know that life is filled with tragedy. Sin is ugly. But I am the God of beauty. I am the God who is able to overcome these things, and I call you away from them to myself.” At the end of the Bible, in Revelation, we have a picture of God sitting on his throne around which is a rainbow. Look forward to that and let God’s beautiful sign minister to your soul. 
 Boice, J. M. (1998). Genesis: an expositional commentary (pp. 388–389). Grand Rapids, MI: Baker Books.