Hagar bare. Through infirmity of Sarah's faith. So the Law (parenthetically) "because of transgression" (Galatians 1:3; Galatians 1:19). Levitical Law given, as Ishmael was, until Christ the antitype of Isaac should be born (Galatians 1:1-5; Galatians 1:19, Gal 1:31).
Related Commentaries of Genesis 16:15
Genesis 16:15
15 And Hagar bare Abram a son: and Abram called his son's name, which Hagar bare, Ishmael.