The hard part of making an A-bomb nowadays is not having the blueprints, machinery, and technical skills but getting enough fissionable material. That means enriching uranium to a relatively high degree, cooking it in a nuclear reactor to make plutonium, chemically extracting the plutonium, and then fashioning it into the implosion device that is the heart of a nuclear bomb.
The Iranian strategy is to become nuclear capable but not quite a nuclear power. That means getting all the necessary elements in place secretly in order to be able to announce at a moment of their choosing via a public statement and an underground nuclear test that they are now a nuclear power with a stockpile of nuclear weapons available for use against the enemies of Iran and Islam.
The closer Iran gets to nuclear capability, the more they become a so-called virtual nuclear power with enhanced strategic heft as if they had bombs in hand but with much less risk that the US or Israel will act against them.
The Iranians, whose national pastime is chess, have the easy parts accomplished and are steadily accumulating a secret supply of highly enriched uranium. By doing so, Iran is getting closer and closer to their strategic goal of becoming nuclear capable without actually making nuclear weapons.
By way of analogy, Iran is acting like a violent, moody, religious nut living just a few houses over from you who is widely known to be accumulating guns and dynamite but who denies doing so. Absent proof, the police can do little.
One day, that religious nut neighbor says that all is ready and that they will no longer accept the disrespect of the neighborhood. They then come to your door and complain about the unkind things being said about them, claim that your well-behaved kids are too loud, and offer religious instruction as a friendly gesture.
Do you tell the religious nut neighbor known to have a large stockpile of guns and dynamite to get lost, or do you disavow any unkind comments from the past, promise to make your kids be quiet, and meekly take up their invite to a prayer meeting? And what will the other neighbors do?
For now, with the world suffering from a desperate shortage of oil and gas, Israel and the US are using word games to avoid a crisis by suggesting a denial that Iran is moving toward nuclear weapons capability. In that manner, Israel and the US are delaying the confrontation with Iran to a better strategic moment. For those who understand the game though, this is only a matter of delaying the confrontation.