"for it is a soul that he takes as a pledge": This is the basis (of the prohibition).
"who steals a soul of his brothers": and not of gentiles;
"of the children of Israel": to exclude one who is half-slave-half-free.
"and he exploits him": He is not liable until he brings him into his domain. R. Yehudah says: (He is not liable) until he brings him into his domain and uses him, as it is written (Ibid.) "and he exploits him and sells him."
"then he shall die": by the unqualified "execution" of the Torah — strangulation.