probably the Orphic poets were the inventors of the name, and they were under the impression that the soul is suffering the punishment of sin, and that the body is an enclosure or prison in which the soul is incarcerated, kept safe (soma, sozetai), as the name soma implies, until the penalty is paid;
Baina niri iruditzen zait batez ere Orfeoren ingurukoek jarri zutela izen hori, arimak bere hutsegiteengatik zigorra betetzen duelakoan, eta itxitura hori daukala, kartzelaren irudira, gorde dadin (sotzetai);