The immediate objective may be a nuclear deal, but I think this is much bigger for Obama. Normalizing relationships with Iran is about his legacy and his view of how the US should engage with the world, even when we fundamentally disagree with a regime.
If he succeeds, Obama's biggest foreign policy legacy will be breaking two of our longest running spats, with Iran and Cuba. He will have moved our relations with these countries from an uncomfortable and tortured deep-freeze to active engagement that reflects a changed world.
In both cases, these countries and peoples have natural ties to the US and its people. Iran has a young, well-educated population and an extremely rich cultural tradition (as evidence I present the insanely good movies they produce). Cuba, of course, is right next door and we've been engaged with them culturally, commercially, and yes militarily for centuries.
In both cases we've been involved in coups to put in place leaders more aligned to US interests. In Iran, the democratically elected president, Mohammed Mosaddegh was overthrown in a coup supported by the CIA. Obama obliquely referred to this in his 2009 speech in Cairo, though some people believe the CIA's role has been overplayed. In Cuba we propped up the military dictator Batista.
Some of this was driven by the mercantile interests of US/British businesses in commodities (Sugar in Cuba, Oil in Iran). In the case of Iran, Mossadegh nationalized the oil industry (which was largely run by British Petroleum till then). In Cuba, Castro's regime nationalized a number of US owned businesses. It is probably not an accident that in both instances we replaced governments that were dismantling feudal holdings and oligarchies. It was, after all, the Cold War.
We have had traumatic experiences with both countries (the Iran Hostage Crisis and the Cuban Missile Crisis). These precipitated the definitive breaks in diplomatic relations.
All this is quickly receding into the past as generations and the nature of the world changes. The concerns we had during the Cold War are no longer the same concerns as Asia develops and a rainbow of revolutions sweep across Central-Asia and the Middle-East. Our interests in both the Middle-East and the Americas would be furthered by engagement with Iran and Cuba respectively since virtually every other country in those regions considers them major players.
I think this is the context in which we must read Obama's Nowruz address (which has become a regular feature of his administration). It is a very, very warm address with a lot of references to Iran and a desire to express both respect and appreciation for Iran's rich culture and traditions, with quotes from Hafez, references to different Iranian towns. It basically signals he has made an effort to go beyond caricatures of Iran.
To quote Obama (from the NY Times):
But a “reasonable deal,” he argues, would lead to “more foreign investment and jobs, including for young Iranians. More cultural exchanges and chances for Iranian students to travel abroad. More partnerships in areas like science and technology and innovation. In other words, a nuclear deal now can help open the door to a brighter future for you — the Iranian people, who, as heirs to a great civilization, have so much to give to the world.”
The more I think about it, the more I believe that for Obama, normalizing relations with Cuba is a dry run for normalizing them with Iran, and both were personal objectives before he became president.
As an aside, Nowruz is a Persian festival with pre-Islamic roots. It's significance in Iranian society is one of the reasons characterizing Iran as a crazed nation entirely populated with hard-line Islamic radicals is sort of ridiculous. Extreme conservatives tried to suppress Nowruz celebrations in Iran after the revolution, but the Iranian people at large weren't having any of that. Even among Shia religious authorities in Iran at the very, very highest levels you find various degrees of liberal humanism.