Pakistan and Iran should forget about their paranoia regarding Afghanistan and should take practical steps for the economic prosperity of Kabul.
Being an Afghan and head of the state President Karzai or his successors would not allow anybody to use this land against neighboring countries. When this very fact is visible to all, then why the two are busy in harping on about their paranoia and belly ache. No one in Afghanistan either s/he be civilian or military person wants to see Tehran and Islamabad in chaotic situations. They should content that Afghan security forces wouldn't take such steps that could lead to anxiety in the region, because we have witnessed worst challenges for many years and know the pain of losing dear and near ones.
However, both Tehran and Islamabad should fulfill their promises to eliminate all anti-Afghanistan elements from their land and take priority based measures to bolster up our economy, which is utmost important to see the region peaceful and live in harmony.
Kabul is aware about the reasons why Iran and Pakistan are worried about Afghanistan. That's why Kabul for several times has categorically annunciated that nobody would be allowed to use this land against any other country, because we share common history, culture and language. If destabilized Afghanistan doesn't go in favor of the region, so is destabilized Pakistan or a troubled Iran. Any patriotic and far-seer Afghan wouldn't let the US or another power to use Afghan soil as a launching pad against Islamabad or Tehran but unfortunately Pakistanis have used their land as a launching pad and as a safe sanctuary for anti-Afghanistan elements.
Now that's up to the wisdom of the respective neighbors to realize this very fact and restrain themselves from such actions that damage national interests of Afghanistan. For instance, supply of huge caches of weapons to the Taliban by Pakistan and Iran has created troubles for Kabul and unleashed tensions in the region. It has brought a deep cleavage among the citizens of the states involved in the game. Even religion, once a unifying force, is unable now to wield the citizens of the three states as one Muslim homogenous.
When there are no regional rivalries Kabul would be very helpful to Islamabad and Tehran to resolve their conflicts with other countries; nevertheless if they keep continue their anti-Afghanistan activities then definitely Kabul will fall into a camp which they don't like. In such a case who is blameworthy? Surely not Kabul.
Kabul could make grounds for Pakistan to come closer to India and resolve their disputes mutually while extending cooperation in all spheres to make South Asian Association for Regional Cooperation (SAARC) a successful organization like European Union, as the trust deficit between the two countries is a big hurdle and not letting SAARC to function which it was designed for.
Besides that Afghanistan could also provide a platform to Tehran to settle the Sunni-Shia conflict with Pakistan once and for all, which is created and fueled by Saudi Arabia with its liberal funds to Pakistan's ISI and extremists elements. Once the Sunni-Shia conflict in Pakistan is subdued it will discourage extremism as sectarianism is a form of it.
Therefore, the promises made by Iran and Islamabad for economic development of Afghanistan in the recent summit held at Tajikistan should come to its tangible and substantial shape or else all have to face the terrible consequences bred by mistrust and selfishness.