46 And he said to them: Thus it is written, and thus it behoved Christ to suffer, and to rise again from the dead, the third day: 47 And that penance and remission of sins should be preached in his name, unto all nations, beginning at Jerusalem. 48 And you are witnesses of these things.
Theophylact: This name of Christ also contains in itself both the Father as the Anointer and the Spirit as the Anointing, and the Son as the Anointed, that is, in His human nature. But it was fitting that the race of man should no longer be divided into Jews and Gentiles, and therefore that He might unite all in one, He commanded that their preaching should begin at Jerusalem but be finished with the Gentiles.
49 And I send the promise of my Father upon you: but stay you in the city till you be endued with power from on high.
Chrysostom: As a general does not permit his soldiers who are about to meet a large number, to go out until they are armed, so also the Lord does not permit His disciples to go forth to the conflict before the descent of the Spirit. And hence He adds, But tarry ye in the city of Jerusalem, until ye be endued with power from on high.
Theophylact: That is, not with human but heavenly power. He said not, until ye receive, but be endued with, showing the entire protection of the spiritual armor.
Chrysostom: Mark also what a necessity He imposed upon them of being at Jerusalem, in that He promised that the Spirit should there be given them. . . . He did not express the time when, in order that they may be constantly watchful.
Gregory: We abide in a city, when we keep ourselves close within the gates of our minds, lest by speaking we wander beyond them; that when we are perfectly endued with divine power, we may then as it were go out beyond ourselves to instruct others.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. III (London: Rivington, 1843).