In Genesis 1:26 we hear the conversation of the Godhead about the creation of humanity:
Then God said, “Let us make man in our image, after our likeness. And let them have dominion over the fish of the sea and over the birds of the heavens and over the livestock and over all the earth and over every creeping thing that creeps on the earth.”
This text has long been treasured by Christians as the teaching of the Trinity in the Old Testament. But this confession has also been disputed.
In Luther’s commentary on Genesis he takes us the arguments for and against this text.
The word “Let Us make” is aimed at making sure the mystery of our faith, by which we believe that from eternity there is one God and that there are three separate Persons in one Godhead: the Father, the Son, and the Holy Spirit. The Jews indeed try in various ways to get around this passage, but they advance nothing sound against it. This passage bothers them to death, to use an expression of Occam, who applies it to irksome and difficult problems which he cannot solve.
Luther will then take up the objections against the Trinitarian reading. There are three other possibilities. God could be talking to the angels, to the earth, or to other creatures.
The Jews, then, say that God is speaking thus with the angels, likewise with the earth and with other creatures.
First, that God is speaking with the angels, Luther offers five points of rebuttal.
But I for my part ask: Why did He not also do this previously? In the second place: What concern is the creation of man to the angels? In the third place: He does not mention the angels but simply says: “We.” Therefore He is speaking of makers and creators. This certainly cannot be said of the angels.
In the fourth place, this is also sure: that it cannot be said in any way that we were created according to the image of the angels. In the fifth place, here both appear: “Let Us make” and “He made,” in the plural and in the singular; thereby Moses clearly and forcibly shows us that within and in the very Godhead and the Creating Essence there is one inseparable and eternal plurality. This not even the gates of hell (Matt. 16:18) can take from us.
Second, regarding the idea that the Lord is speaking to the earth, Luther argues
Next, when the Jews say that God is speaking with the earth concerning the earth, this is also worthless. For the earth is not our maker.
This also applies to the idea that the Lord was speaking to other creatures or parts of creation.
Moreover, why didn’t He rather speak to the sun, since Aristotle says: “Man and the sun bring man into existence.” But this does not fit either, because we were not made according to the image of the earth; but we were made according to the image of those Makers who say “Let Us make.” These Makers are three separate Persons in one divine essence. Of these three Persons we are the image, as we shall hear later.
Finally, another objection is offered, namely that to say “We” and “us” is a custom of royalty, and does not indicate plurality. Luther repsonds
It is utterly ridiculous when the Jews say that God is following the custom of princes, who, to indicate respect, speak of themselves in the plural number. The Holy Spirit is not imitating this court mannerism (to give it this name); nor does Holy Scripture sanction this manner of speech.
The conclusion, then, is a bold and comforting doctrine of the Holy Trinity. We rejoice in the “Let us make,” knowing that our first parents were created in the image and likeness of God.
Consequently, this is a sure indication of the Trinity, that in one divine essence there are three Persons: the Father, the Son, and the Holy Spirit. Not even so far as Their activity is concerned, therefore, is God separated, because all three Persons here co-operate and say: “Let Us make.” The Father does not make one man and the Son another, nor the Son one man and the Holy Spirit another; but the Father, the Son, and the Holy Spirit, one and the same God, is the Author and Creator of the same work.
The quotations may be found here: Martin Luther, Luther’s Works, Vol. 1: Lectures on Genesis: Chapters 1-5, ed. Jaroslav Jan Pelikan, Hilton C. Oswald, and Helmut T. Lehmann, vol. 1 (Saint Louis: Concordia Publishing House, 1999), 57–58. Order from CPH. Or you can read an older translation of the Genesis commentary online here.