Why is the ninth month called September?
"the elect, the select," especially those selected by God, c.1200, from past participle of choose (v.). Chosen people for "the Jews" is recorded from 1530s.
Old English ceosan "choose, seek out, select; decide, test, taste, try; accept, approve" (class II strong verb; past tense ceas, past participle coren), from Proto-Germanic *keus- (cf. Old Frisian kiasa, Old Saxon kiosan, Dutch kiezen, Old High German kiosan, German kiesen, Old Norse kjosa, Gothic kiusan "choose," Gothic kausjan "to taste, test"), from PIE root *geus- "to taste, relish" (see gusto). Only remotely related to choice. Variant spelling chuse is Middle English, very frequent 16c.-18c. The irregular past participle leveled out to chosen by 1200.
spoken of warriors (Ex. 15:4; Judg. 20:16), of the Hebrew nation (Ps. 105:43; Deut. 7:7), of Jerusalem as the seat of the temple (1 Kings 11:13). Christ is the "chosen" of God (Isa. 42:1); and the apostles are "chosen" for their work (Acts 10:41). It is said with regard to those who do not profit by their opportunities that "many are called, but few are chosen" (Matt. 20:16). (See ELECTION.)