Hazrat Moulana Ashraf Ali Thanwi (rahmatullahi ‘alaih) once mentioned:

The effect of imaan in the life of a person is such that it prompts him towards showing kindness and compassion to the creation, forgiving and overlooking their weaknesses and adopting courage and bravery at the time of difficulties. As a result of not possessing Imaan, these qualities are not seen in the kuffaar. (Malfoozaat Hakeemul Ummat 8/136)

Source: Ihyaauddeen.co.za