ISB ~ Matthew 10 v28

do not fear:Human agents of persecution are not to be feared. Men can impose suffering and death on the body but cannot force spiritual death on the soul. Jesus uses this distinction between body and soul to contrast the relative value of earthly life with the absolute good of eternal life in heaven (CCC 363).

rather fear him:Since Satan deceives and tempts souls into sin, he should be feared and resisted as our worst enemy (Eph 6:11; Jas 4:7; 1 Pet 5:8-10). In view of the similar expression in Is 8:12-13, God should also be feared. He alone administers perfect justice and can send the faithless to eternal punishment (3:12; 25:41). A holy fear of God is thus necessary to avoid sin and its consequences (Ex 20:20; Phil 2:12).