Because Zhang Xueliang once owed Dai Li a "famous debt". During Zhang Xueliang's drug rehabilitation period, Dai Li and others saved Zhang's family many times from the Japanese. This can be said to be a life-saving grace, so this human debt Naturally, Zhang Xueliang must be blamed.
Dai Li is also a smart man. He knew that although Zhang Xueliang was already under house arrest at the time, it would be easy for him to lend him a gun. Moreover, he believed that Zhang Xueliang was also a kind and righteous person, and he could not refuse his request even for the sake of his kindness in saving Zhang's life.
Sure enough, Dai Li mentioned borrowing a gun in front of Zhang Xueliang, and Zhang Xueliang agreed after a moment of hesitation. After all, they are all Chinese. Although they are not in the same army, they are all going to fight the Japanese. Even a man with some flesh and blood will not ignore death.
After all, anyone living in this world may encounter difficulties, and anyone may receive help from others. Only when you help others will you have more blessings. Zhang Xueliang lent the gun to Dai Li in the hope that Dai Li could kill more enemies in the front.