This might not be totally correct, but new interpretations of the Constitution are commonly formed when someone's statements on issues do not align perfectly with what the Constitution states. Therefore, a new interpretation of the Constitution is offered up in an attempt to clear up the Constitution's stance on the matter, or to support the person's stance. For example, say a politician stated that the Constitution did not actually allow one of the rights stated in it. They would be offering up a new interpretation of the Constitution. I hope this helps!