When God makes a promise to us, it has to be true. He cannot promise anything that isn’t true. The great flood of the Old Testament signified the end of the old world. The new world that we live in, is a world of God’s mercy.
As the old world was ruined, to be a monument of justice, so this world remains to this day a monument of mercy. But sin, that drowned the old world, will burn this. The seal of this covenant was the rainbow, which, it is likely, was seen in the clouds before, but was never a seal of the covenant till now it was made so. The rainbow appears when we have most reason to fear the rain prevailing; God then shows this seal of the promise, that it shall not prevail. The thicker the cloud, the brighter the bow in the cloud. Thus, as threatening afflictions abound, encouraging consolations much more abound. The rainbow is the reflection of the beams of the sun shining upon or through the drops of rain: all the glory of the seals of the covenant are derived from Christ, the Sun of righteousness. And he will shed a glory on the tears of his saints.