Western civilisation has been ruled and matured by Christian thought to such an extent that any act of charity by anybody is called a Christian act. Psychologists inform us that such acts are not truly altruistic but make us feel good and inflate our ego's.
Jesus was well aware of this hence the story of the widows mite and his warning to ' give alms in secret.
Evan so the Christian believes he is ' laying by treasure in heaven.
So perhaps the noblest Christian act is that performed by an unbeliever in secret , who has nothing to gain.
The question of reward , which is linked to justice is summed up neatly : steak on the plate or pie in tbe sky.
Firebrand Christians totally give up steak on the plate for pie in the sky. Such behaviour hardly fits with human nature and the vast magority balance these two clinging to both.
Its the best of both worlds senario and Christian theology has been honed considerably to fit.
Isis is a throw back to the crusades where pie in the sky makes killing a virtue. Yet to attract followers there needs to be plenty of Islamic steak on the plate.