Karma moves consciousness between the realms. Karma refers to the influences of the past, wholesome or unwholesome. The forces from the past impact on consciousness in the present.
The Buddha emphasised on the importance of the understanding of kamma. He said:
“Karma (kamma in Pali) should be understood
The diversity of karma should be understood
The result of karma should be understood
The cessation of karma should be understood
The way leading to the cessation of karma should be understood
For it is volition that I call karma. For having will, one acts by body, speech and mind.” AN 6.63.
The cessation of karma refers to the cessation of contact. A simple example: There is the volition to smoke which becomes an addiction. Smoking becomes an abuse of body and mind. Based on habits, the smoker makes frequent contact with cigarettes. Despite years of apparent grace or incubation period, the results of karma eventually land in consciousness, such as a cancer.
The smoker stops the contact with cigarettes. This is the end of the karma, the volition., the will. The cessation of contact may well be early enough for many to stop the impending cancer.
These forces of karma can move consciousness to heavenly realms of the gods and angels or to the hellish realms of asuras and hungry ghosts. Due to intense craving, hungry ghosts never know satisfaction or any kind of fulfilment. We need to understand that the Buddha referred to the realms to show a way to make sense of the changes in consciousness from the ordinary experiences of humans, to being in heaven or to plunging into a hellish way of life.
This world contains all types of presences, not just human beings in touch with the senses, nor animals often stuck in their biological make up. A human being has the basic resources for full awaking, namely consciousness/mind/body/knowledge of inner/outer and the capacity to change.