The scientific part of the analogy of the rainbow is of course obsolete and valueless.  The general principle holds good that what is beyond comprehension in theology finds its parallel in what is beyond comprehension in the visible world.  We are not to be staggered and turn dizzy in either sphere of thought at the discovery that we have reached a limit beyond which thought cannot go.  We may live in a finite world, though infinite space is beyond our powers of thought:  we may trust in God revealed in the Trinity, though we cannot analyse or define Him.