By the name Lord is meant the Savior of the world, Jesus Christ, and Him only; and He is called “the Lord” without the addition of other names. Throughout the universal heaven He it is who is acknowledged and adored as Lord, because He has all sovereign power in the heavens and on earth. He also commanded His disciples so to call Him, saying, Ye call Me Lord, and ye say well, for I am (John 13:13). And after His resurrection His disciples called Him “the Lord.” (Arcana Cœlestia 14)
Among the hidden causes of their calling Jehovah “the Lord” were the following. If at that time it had been said that the Lord was the Jehovah so often named in the Old Testament, men would not have accepted it, for they would not have believed it; and moreover –
The Lord did not become Jehovah as to the Human also until He had completely united the Divine Essence to the Human Essence, and the Human to the Divine.
The full unition was accomplished after the last temptation, which was that of the cross; and for this reason, after the resurrection the disciples always called Him “the Lord” (John 20:2, 13, 15, 18, 20, 25; 21:7, 12, 15-17, 20; Mark 16:19, 20); and Thomas said, My Lord and my God (John 20:28).
And because the Lord was the Jehovah so often named in the Old Testament, He therefore also said to the disciples:
Ye call Me Master and Lord, and ye say well, for I am (John 13:13-14, 16)
and these words signify that He was Jehovah God; for He is here called “Lord” as to good, and “Master” as to truth. That the Lord was Jehovah is also meant by the words of the angel to the shepherds:
Unto you is born this day a Saviour who is Christ the Lord (Luke 2:11)
He is called “Christ” as the Messiah, the Anointed, King; and “Lord” as Jehovah; “Christ” in respect to truth, and “Lord” in respect to good. One who does not closely study the Word could not know this, for he would think that our Savior was called Lord, like others, from the common title of reverence; when yet He was so called because He was Jehovah. (Arcana Cœlestia 2921:6)
And he lifted up his eyes, and saw, and behold three men standing over him; and he saw them, and ran to meet them from the door of the tent, and bowed himself toward the earth. (Genesis 18:2)
That this signifies the Divine Itself, the Divine Human, and the Holy proceeding, may be seen without explication; for it is known to everyone that there is a Trine, and that this Trine is a One. (Arcana Cœlestia 2149)
And he said, My Lord, if I pray I have found grace in Thine eyes, pass not I pray from Thy servant. (Genesis 18:3)
My Lord. That this signifies the Trine in a One, namely, the Divine Itself, the Divine Human, and the Holy proceeding, which Trine is in a One, is evident from its being here said “Lord,” in the singular number. … Hence it is evident that the three men (that is, the Divine Itself, the Divine Human, and the Holy proceeding), are the same as the Lord, and the Lord the same as Jehovah.
In the Christian Faith, called the Creed, the same is acknowledged, where it is said in plain words, –
“There are not three Uncreate, nor three Infinite, nor three Eternal, nor three Almighty, nor three Lords, but One.”
There are none who separate this Trine which is in a One except those who say that they acknowledge one Supreme Existence [Ens], the Creator of the Universe; which is forgiven those who are outside of the church. But they who are within the church, and say this, although they say it and sometimes think it, do not in fact acknowledge any God; still less do they acknowledge the Lord. (Arcana Cœlestia 2156)