"Let not the Unbelievers think that they can get the better (of the godly): they will never frustrate (them). Against them make ready your strength to the utmost of your power, including steeds of war, to strike terror into (the hearts of) the enemies, of Allah and your enemies, and others besides, whom you may not know, but whom Allah knows. Whatever you shall spend in the Cause of Allah, shall be repaid to you, and you shall not be treated unjustly"[Qur'an 8:59-60]
This one says to me to ready whatever weapons you have against the Unbelievers. al-Qaida (and Hamas etc...)doesn't have much (compared to the USA) but it still makes ready for war. UBL clearly believes he will be rewarded greatly in the hereafter due to the vast fortune he has spent "in the cause of Allah".