But then it was the good pleasure of God, who set me apart [for this purpose] before I was born, to call me [to this ministry] through His unearned favor.

But, when [God's] timing fully arrived, He sent His Son, born to a woman [i.e., Mary], born during [the time when] the law [of Moses was still in effect],

Now the son [Ishmael], born to the slave woman, was born simply of their natural relationship; but the son [Isaac], born to the free woman, was born in fulfillment of a [divine] promise.

But, just as it was then --- the son born in the ordinary way [i.e., Ishmael] persecuting the one born according to the Holy Spirit's [leading, i.e., Isaac] --- so it is now [i.e., Jews urging compliance with the requirements of the law of Moses persecuting those who refuse to return to dependance on that law for salvation. See 3:1-3].