What does the expression “χριστὸν τοῦ θεοῦ” mean in Peter’s mind, used in Luke 9:20 in reference to 2 Samuel 23:1 LXX mean?

These are the final words of David: "The oracle of David son of Jesse, the oracle of the man raised up as the ruler chosen by the God of Jacob, Israel’s beloved singer of songs: NET 2 Samuel 23:1 καὶ οὗτοι οἱ λόγοι Δαυιδ οἱ ἔσχατο…