The very last image the viewer is presented with reveals the purpose of the advertisement. After the viewer has felt the pain cancer can cause and the joy of a life without it, they are asked to donate to the cause of making even more lives be like the mother and child at the end of the video as opposed to the lonely child at the beginning. Additionally, the choice of the color blue as the background is an appeal to ethos. Just as statistics suggest credibility, the color blue represents and instills loyalty, trust, and confidence. This final image the suggests that Cancer Research UK is a reputable company and can be trusted with donations.
Through this advertisement, Cancer Research UK does a magnificent job in convincing its audience to donate. However, in asking for a continuing monthly donation, the foundation could lose many of its potential donors. People are often very susceptible to giving a one time donation, especially if they think it is for a good cause and it will make them feel better about their own morals. However, often people will be reluctant to make a longtime financial commitment because their initial emotional response will most likely only last for a short time after the advertisement has ended.
Reference here to learn more about color meanings and associations.