All who rely on ... the law are under a curse

Being under a curse represents being cursed. Here it refers to being eternally punished. "Those who rely on ... the law are cursed" or "God will eternally punish those who rely on ... the law" (See: rc://en/ta/man/translate/figs-metaphor and rc://en/ta/man/translate/figs-metonymy)

the works of the law

"what the law says we must do"