Such distinctions, resting as they must on an idea of the self as being (ideally) homogenous, non-hybrid, 'pure,' - and utterly fantastic notion! - cannot, must not, suffice (442).
This passage indicates the distinction in the forms that Gibreel and Saladin have taken. Gibreel has taken on his angelic form because, in the eyes of the colonizer, he does not attempt to assimilate into the English culture and holds onto his own and his past. Saladin has a demonic form because he is vying to adopt the culture of the English and reject Indian culture. The colonizer is not threatened because their own culture is preserved. Though he is considered "good," he is still considered inferior. He may not be treated horribly like Saladin, but he is not treated as an equal either. The English culture is still "homogenous, non-hybrid," and "pure." Saladin, however, seeks to become "English." Such an act is offensive to the colonizer because the colonized considers himself good enough to emulate the colonizer. For example, when the immigration officers apprehend Saladin after the plane crash, he attempts to identify himself as an English citizen, even saying he has a white wife, and they simply abuse him more.
The English reject Saladin as an Englishmen, even though he has crafted every detail about himself emulate an English citizen almost perfectly. The greatest offense, however, is the color of Saladin's skin. Race is part of the Essentialism, or a set of defining characteristics unique to one group of people. In this case, whiteness is almost parallel to being English. The purity is in danger of being contaminated because Saladin is originally Indian. India was also a former colony, so the English are excluding them from their culture to assert their superiority since they lost their physical domination of the people and the country. Saladin's and Gibreel's forms represent the way the English people see them in relation to the danger they pose to the purity, non-hybridization, and homogeneity of English culture and identity.