Paul claims to have been separated by God’s good pleasure from his mother’s womb (Galatians 1:15; Gr. koilias metros ), so that the Son could be unveiled ( apokalupsai ) in him.  There’s a rich Old Testament background.

Most obvious is the link with Jeremiah, who is also separated from his mother’s womb as a prophet to the nations (Jeremiah 1:5), as Paul is separated out to be a prophet to the Gentiles.  That is quite precisely the sequence of Paul’s thought: “the one who separated me from my mother’s womb . . . that I might evangelize among the nations” (Galatians 1:15-16).

But Paul is also a Samson, who was a separated Nazirite from his mother’s womb (Judges 16:17).  And, Paul is linking himself to the servant of Yahweh, called and named from his mother’s womb, equipped with a sharp sword in his mouth, made an arrow of the Lord (Isaiah 49:1-2).  Isaiah 49:3 is revealing:

The Servant is called from the womb so that in him Yahweh can show His glory.  Paul is again quite precisely following this sequence: “the one who separated me from my mother’s womb and called me through His grace to unveil His Son in me” (Galatians 1:15-16).  The Son is Yahweh’s glory unveiled in his servant Paul.  As Isaiah 49 goes on, it too incorporates the mission to the nations.  49:5 reiterates that Yahweh has formed the Servant from the womb, and assures the servant that He will bring back Jacob.  Ultimately, this is too small a thing: “I will also make you a light of the nations, so that my salvation may reach to the end of the earth” (v. 6).

G. Walter Hansen points out ( The Galatians Debate: Contemporary Issues in Rhetorical and Historical Interpretation ) that prophetic echoes are also evident in the “not, nor . . . but” structure of both Galatians 1:1 and 1:11-12.   Hansen hears echoes of Amos 7:14-15 and Jeremiah 14:14 in these verses.  Further, Hansen points out that Paul uses the word apokalupsis twice in the passage (vv. 12, 16), which refers to an unveiling of God’s glory and a decisive intervention by God into history.  According to Paul, his own ministry began (like Ezekiel’s, for instance) with an apocalypse of the glory of God in the Son, and his ministry is to be an instrument of that unveiling.