Iran is a messianic theocracy. Ever looked at a map of the region? It has enough conventional military power to close the Straits of Hormuz tomorrow and dictate the flow of 40% of the world's oil, turn the Gulf states into colonies and stifle the international influence of Sunni Saudi Arabia. However, the west would fight to preserve such a direct attack on its way of life. With nuclear weapons Iran can do what it likes with its neighbours and the world oil supply, with impunity. Acquiring nuclear weapons is therefore a national interest for a messianic theocracy like Iran. BTW, in the short term, America has more to fear from a nuclear Iran than Israel.
Saudi-led planes hit Houthi-controlled government buildings (Reuters)
from the article: U.S. Defense Secretary: Iran could get nuclear bomb within a year