God's Promise
76.18 κυρόωa: to invest something with power or force—‘to give force to, to validate.’ κεκυρωμένην διαθήκην οὐδεὶς ἀθετεῖ ‘no one sets aside an agreement which has been put into force’ or ‘no one sets aside a covenant which has been validated’ Ga 3:15. In order to express the meaning of this phrase in Ga 3:15, it may be necessary in some languages to make more specific the arrangements involved, for example, ‘if people have signed an agreement, no one can disregard it’ or ‘if an agreement has been confirmed, no one can say it does not exist’ or, as in some languages, ‘if an agreement has been tied, no one can untie it.’
Paul’s willingness to make an argument using a singular noun in distinction from its plural form (which occurs in other OT verses) indicates a high level of confidence in the trustworthiness of the small details of the OT text