A.T. Robertson Commentary Galatians 3:10

"For as many as are of the works of the law are under a curse: for it is written, Cursed is every one who continueth not in all things that are written in the book of the law, to do them." — Galatians 3:10 (ASV)

Under a curse (υπο καταραν). Picture of the curse hanging over them like a Damocles' blade. Cf. Romans 3:9 "under sin" (υφ' αμαρτιαν). The word for "curse" (καταρα) is an old one (κατα, down, αρα, imprecation), often in LXX, in N.T. only here and 13; James 3:10; 2 Peter 2:14. Paul quotes De 27:26, the close of the curses on Mt. Ebal. He makes a slight explanatory modification of the LXX changing λογοις to γεγραμμενοις εν τω βιβλιω. The idea is made clearer by the participle (γεγραμμενοις) and βιβλιω (book). The curse becomes effective only when the law is violated.

Cursed (επικαταρατος). Verbal adjective from επικαταραομα, to imprecate curses, late word, common in LXX. In N.T. only here and verse 13, but in inscriptions also (Deissmann, Light from the Ancient East, p. 96). The emphasis is on "continueth" (εμμενε) and "all" (πασιν).