If it were the case that the five aggregates constituted a being, then this would be a case where they would be born naturally and die naturally just like grass or trees. If this were actually the case, then there would be no being bound by offenses nor would there be any liberation. On account of this one knows that it is not the case that the five aggregates constitute a being. If one asserts that a being exists apart from the five aggregates this constitutes a falling into eternalism. If one falls into eternalism this then entails the nonexistence of birth and the nonexistence of death.
Birth refers to something having formerly been nonexistent now coming into existence.
Death refers to something already born then being extinguished. If it were the case that beings were eternally-existent then it ought to be the case that they exist everywhere filling up the five paths of rebirth. And if it does not have a birth then it has no death either. It is based on the causes and conditions of the five aggregates that the dharma of a being exists. This is analogous to the case of the causes and conditions of the five fingers generating the dharma of a fist.