What did David prophesy about Christ in the Psalms Peter quotes in Acts 2?

Peter cites David in the Psalms, where David prophesies Christ's coming, death, and resurrection. The prophecy was not yet about salvation of Gentiles; it was so all things could be fulfilled for Christ to be Israel's Redeemer, with Israel then passing it to surrounding nations as priests.

Les explains that on the day of Pentecost, seven weeks after the resurrection, Peter addresses “Ye men of Israel,” not Gentiles. Jesus of Nazareth was approved by God among them through miracles, wonders, and signs to prove He was the promised Messiah and King, ready to give Israel the kingdom, and to be their Redeemer. Then in Acts 2:25-30, Peter goes back into the Psalms and quotes David. David speaks prophetically concerning Christ's coming, death, and resurrection. At that point, however, the prophecy is not yet about the salvation of Gentiles. It was given so that everything could be fulfilled, so Christ could be the Redeemer of Israel, and so Israel could then pass it out to the nations around them and be priests.

Acts 2:25

For David speaketh concerning him, I foresaw the Lord always before my face, for he is on my right hand, that I should not be moved:

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What does David speak about prophetically in the Psalms quoted in Acts 2?

In the Psalms quoted in Acts 2, David speaks prophetically of Christ's coming, His death, and His resurrection. This was not yet the salvation of Gentiles, but so everything could be fulfilled for Him to be Israel's Redeemer, and for Israel to pass it out to surrounding nations and be priests.