Egyptian funerary religion does not treat death as a passage into an already-finished afterlife state; it treats death as the start of a transformation that has to be actively accomplished, through correct ritual, correct recitation and correct preservation of the body, and the akh is the name for what a person becomes if that transformation succeeds. The Pyramid Texts, Egypt's oldest substantial religious corpus, are largely organised around securing exactly this outcome for the king: becoming an akh, joining the imperishable stars, the circumpolar stars that never set below the horizon and were taken as a natural symbol of a state beyond further death.
Becoming an akh specifically requires the ka and ba to be successfully reunited, which in turn requires the body itself to survive as a recognisable anchor, correct offerings to keep the ka sustained, and correct knowledge, the spells and formulae of texts like the Pyramid Texts, the Coffin Texts and later the Book of the Dead, to navigate the dangers of the transition. Failure at any stage risked what the Egyptians described as a second death, an irreversible dissolution rather than transfiguration, which is why so much of the surviving textual record is devoted to guaranteeing the akh state rather than merely describing it.
The word akh itself carries a sense of being effective or useful, and an akh who had achieved this transfigured state was believed genuinely capable of affecting the world of the living, which distinguishes it sharply from a merely surviving ka or ba: the akh is not simply a soul that persists, it is a soul that has become powerful.