A.T. Robertson Commentary Galatians 4:25

"Now this Hagar is mount Sinai in Arabia and answereth to the Jerusalem that now is: for she is in bondage with her children." — Galatians 4:25 (ASV)

This Hagar (το Hαγαρ). Neuter article and so referring to the word Hagar (not to the woman, η Hagar) as applied to the mountain. There is great variety in the MSS. here. The Arabians are descendants of Abraham and Hagar (her name meaning wanderer or fugitive).

Answereth to (συντοιχε). Late word in Polybius for keeping step in line (military term) and in papyri in figurative sense as here. Lightfoot refers to the Pythagorean parallels of opposing principles (συνστοιχια) as shown here by Paul (Hagar and Sarah, Ishmael and Isaac, the old covenant and the new covenant, the earthly Jerusalem and the heavenly Jerusalem). That is true, and there is a correlative correspondence as the line is carried on.