2 “O clap your hands, all you nations”. Were the people of the Jews all the nations? No, but blindness in part is happened to Israel, that senseless children might cry, “Calve,” “Calve;” and so the Lord might be crucified in the place of Calvary, that by His Blood shed He might redeem the Gentiles, and that might be fulfilled which says the Apostle, “Blindness in part is happened unto Israel, until the fullness of the Gentiles be come in.” Let them insult, then, the vain, and foolish, and senseless, and say, “Calve,” “Calve;” but you redeemed by His Blood which was shed in the place of Calvary, say, “O clap your hands, all you nations;” because to you has come down the Grace of God.
“O clap your hands.” What is “O clap”? Rejoice. But wherefore with the hands? Because with good works. Do not rejoice with the mouth while idle with the hands. If you rejoice, “clap your hands.” The hands of the nations let Him see, who joys has deigned to give them. What is, the hands of the nations? The acts of them doing good works. “O clap your hands, all you nations: shout unto God with the voice of triumph.” Both with voice and with hands. If with the voice only it is not well, because the hands are slow; if only with the hands it is not well, because the tongue is mute. Agree together must the hands and tongue. Let this confess, these work. “Shout unto God with the voice of triumph.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)