Are SDAs Christians? Why don't they celebrate Sunday, the day Jesus Christ resurrected?

They should. The early Christians recognized that their weekly celebration of the m- the ongoing re-presentation of Christ's pion, death and resurrection was more appropriately carried out on Sunday. They also realized the necessity of differentiating themselves from the Jews, beginning with the immediate abandonment of Judaism's system of ritual animal sacrifices, and the gradual abandonment of circision, ceremonial rituals. food laws and dietary restrictions imposed by the Law of Moses. They also dispensed with the observance of the Pover and other Jewish feast days.