The Lord,… the Lord,… the Lord. Are we to see in this threefold use of the Divine name a shadowing forth of the Holy Trinity? It is obvious that it cannot be proved, and that it would not even have suggested any such idea to the priest who gave, or to the people who received, the benediction.
To them the threefold form merely added beauty and fullness to the blessing (cf. Ecclesiastes 4:12). But that is not the question. The real question is whether the Old Testament was written for our sakes (1 Corinthians 9:10; 1 Corinthians 10:11; 2 Timothy 3:15, 2 Timothy 3:16), and whether the God of the Jews was indeed the Father of our Lord Jesus Christ (John 5:17; John 8:54).
If so, it is not possible for us to avoid seeing in this benediction a declaration of the threefold Being of God, and it is not possible to avoid believing that he meant us to see such a declaration, veiled indeed from the eyes of the Jew, but clear enough to the Christian.
For a somewhat similar case compare Isaiah 6:3; Revelation 4:8.