3 “He has remembered His mercy to Jacob, and His truth unto the house of Israel”. What means this, “He has remembered His mercy and truth”? He has pitied, so that He promised; because He promised and showed His mercy, truth has followed: mercy has gone before promise, promise has been fulfilled in truth....
“And His truth unto the house of Israel.” Who is this Israel? That ye may not perchance think of one nation of the Jews, hear what follows: “All the ends of the world have seen the salvation of our God.” It is not said, all the earth: but, “all the ends of the world:” as it is said, from one end to the other. Let no man cut this down, let no man scatter it abroad; strong is the unity of Christ. He who gave so great a price, has bought the whole: “All the ends of the world.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)