From eternity, Jesus Christ was God the Son. He humbled Himself and became Man (see Phil. 2:5–6). In His resurrection, however, He glorified that humanity received from the Father and received back the eternal glory He had veiled (John 17:1, 5). The Resurrection declares: “Jesus is God’s Son!” (Rom. 1:4)
The original context of the psalm was quite different, referring to the marriage feast of some king of Israel. Yet it was widely recognized to have a much more extended meaning and was in fact regarded as Messianic. It is in this latter sense that it is here quoted.