Why do the blood types of a person providing blood for a transfusion, and the person receiving the blood, have to be of a compatible abo type?

Blood transfusion involves removing blood from a blood donor and giving it to another person to replace blood loss. Making safe blood transfusion is essential to know the blood type of the patient. because mixing incompatible blood types may cause to danger and lethal. To be successful in blood transfusion, ABO and RH blood of a donor and a patient. If a blood transfusion gets wrong, it may lead to immunological reactions, it occurs when a receiver of blood transfusion has antibodies that work against to the blood cells of a donor.