The pledge binding al-Qaeda to the Taliban

Al-Qaeda is bound to the Taliban by a pledge of allegiance — or “bay’ah” — which was first offered in the 1990s by Osama Bin Laden to his Taliban counterpart Mullah Omar.
The pledge has been renewed several times since, although it has not always been publicly acknowledged by the Taliban.
So what is the significance of this pledge?
It entails obligations for both parties, including obedience by the one offering bay’ah to a leader. Reneging on the pledge is considered a serious offence in Islam.
With their return to power, the Taliban are now being pulled in two directions.
Their ties to al-Qaeda lend the Taliban credibility within hardline jihadist circles, and the historic loyalty towards al-Qaeda means they may not be keen to abandon their ally now they hold power.