J. Louis Martyn ( Galatians (The Anchor Yale Bible Commentaries) ) notes Paul’s fourfold use of “apocalypse” in Galatians (1:12 15-16; 2:2; 3:23).  Paul received his gospel “when God apocalypsed Christ to him,” and this gospel was about the “apocalypse” of faith (3:23), which Paul described as a “coming” and a “sending” of faith, of the Son and Spirit (4:4, 6).

Martyn does not think “unveil” captures Paul’s idea.  Rather, the image is one of invasion: “The genesis of Paul’s apocalyptic . . . lies in the apostle’s certainty that God has invaded the present evil age by sending Christ and his Spirit into it.  There was a ‘before,’ the time when we were confined, imprisoned; and there is an ‘after,’ the time of our deliverance.  And the difference between the two is caused not by an unveiling, but rather by the coming of Christ and his Spirit.”

The structure of Paul’s reception of the gospel is the same as the structure of the gospel itself - both involve an apocalyptic coming of the Son.  Thus Paul becomes the one in whom the Father has chosen to display His glory.