Tertullian

Hence the apostle refers the statement to himself, that is, to the Jews, in order that he may draw a distinction with respect to the Gentiles, (when he goes on to say: ) "In whom ye also trusted, after that ye heard the word of truth, the gospel (of your salvation); in whom ye believed, and were sealed with His Holy Spirit of promise." Of what promise? That which was made through Joel: "In the last days will I pour out of my Spirit upon all flesh," that is, on all nations.