The Lord’s "own" are those who have His Word and know him, the heart and center of His contact with humanity. This has existed in various forms since the dawn of humanity, but at the time the Lord was born as Jesus it meant the Jews, who worshiped the Lord as Jehovah and had His truth in the form of the laws of Moses, the history of their own nation and the psalms and prophets. But the Jews of the time had turned away from the Lord, practicing ritual but looking only to their own selfish ends. In fact, the evil there had grown so dire that humanity was in danger of being cut off from the Lord altogether; if He had not come as Jesus we would have been destroyed altogether.

(References: Arcana Coelestia 2531 [4], 8768; Teachings about the Lord 18 [5]; The Apocalypse Explained 745 [4])