What is the point of the rainbow? What does it symbolize?
Many Christians know from the church's teaching on the flood of Noah's day, that the rainbow originally was a sign of God's promise not to destroy the world by water again. It is this understanding that makes the modern co-opting of the rainbow symbol for gay pride (etc.) seem so egregious. But the rainbow is a symbol of justice too.
“Behold, I establish my covenant with you and your offspring after you,” . . . And God said, “This is the sign of the covenant that I make between me and you and every living creature that is with you, for all future generations: I have set my bow in the cloud, and it shall be a sign of the covenant between me and the earth.” (Gen. 9:9, 12–13)
The rainbow now designated the sign of God’s promise not to visit wrath on the earth by way of a flood again. But larger than that, the rainbow is another sign of God’s promise to remove his wrath from his children.
The Hebrew word for bow in this text is the same Hebrew word used for the kind of bow one uses in battle, as in “bow and arrows.” What God is talking about is laying down his weapons. In his commentary on Genesis, Marcus Dods writes:
They accepted it as a sign that God has no pleasure in destruction, that He does not give way to moods, that He does not always chide, that if weeping may endure for a night joy is sure to follow. If any one is under a cloud, leading a joyless, hopeless, heartless life, if any one has much apparent reason to suppose that God has given him up to catastrophe, and lets things run as they may, there is some satisfaction in reading this natural emblem and recognising that without the cloud, nay, without the cloud breaking into heavy sweeping rains, there cannot be the bow, and that no cloud of God’s sending is permanent, but will one day give place to unclouded joy.
We keep seeking peace, peace, where there is no peace, and we only find our true lasting eternal joy-saturated peace when it comes by the Spirit of God straight from Father God in the gospel of the Son of God. It is in Christ Jesus’s work that we see that God “lays down his bow.”
And we can keep seeking peace even in God’s good gifts—work, family, recreation, food, art and culture, the great outdoors, and sexual "freedom"—but we can’t find the peace that endures forever until we find it in the gospel. Because justice, while ordained by God, when administered by man can never truly satisfy.
But the covenant of grace is administered by God himself. So when we seek peace there, we truly find it. It’s not tainted by sin because God is holy and his Son is sinless.
Until we find peace in the gospel, we find only the search for peace and therefore no peace at all. In Isaiah 57:21 we read, “There is no peace . . . for the wicked.”
But to those who’ve put on Christ’s righteousness, who’ve gotten into the ark of the cross, Isaiah 26:3 says: “You keep him in perfect peace whose mind is stayed on you, because he trusts in you.”
The rainbow, then, is a sign of God’s promise that he has hung up his bow, and it’s a reminder to himself of his grace toward the earth. In the same way, the cross is a sign of God’s promise that he has hung his Son up to die, and it’s a reminder of his grace toward you that because Christ has taken the wrath, the wrath is taken.
To tout the rainbow, then, as a symbol of man-centered pride, is to urge the Lord, actually, to take up his bow again, to take it back in hand and draw it back. Celebrating pride is a courting of condemnation.
Therefore it says, “God opposes the proud, but gives grace to the humble.” — James 4:6
Put to death therefore what is earthly in you: sexual immorality, impurity, passion, evil desire, and covetousness, which is idolatry. On account of these the wrath of God is coming. — Colossians 3:5-6
A variation on this material appears in The Story of Everything, coming this fall from Crossway.