Paul may have used typology in Galatians 4 because
(1)the false teachers had used this same approach to their advantage, claiming to be the true seed of Abraham
(2)the false teachers may have used an allegory from Moses' writings to push their Jewish
covenant theology so Paul uses the father of the Jewish faith, Abraham
(3)Paul may have used it because of Gen. 21:9-10, which is quoted in verse 30 and says, "drive off" the natural
son; in Paul's analogy this would refer to the Judaizers (see
SPECIAL TOPIC: JUDAIZERS)
(4)Paul may have used it because of the exclusivism of the Jewish false teachers, particularly in their
contempt for the Gentiles; in Paul's typology the Gentiles are accepted (cf. Rom. 2:28-29; Gal. 3:28-29; Eph. 2:11; 3:13;
Phil. 3:3; Col. 2:11) and the racially confident ones are rejected by God (cf. Matt. 8:11-12)
(5)Paul may have used this typology because he has been emphasizing "sonship" and "heirship" in
Galatians 3; 4. This was the heart of his argument: our adoption into the family of God by faith through Christ alone, not natural descent.