"To make such a profound matter somewhat intelligible, the doctors,
particularly Bonaventure, adduce a crude illustration. If, for example, three
young women would take a dress and put it on one of their number and this one
would also take part in clothing herself with this dress, then one could say
that all three were dressing her; and yet only one is being attired in the
dress and not the other two. Similarly we must understand here that all three
Persons, as one God, created the one humanity, clothed the Son in this, and
united it with His person, so that only the Son became man, and not the Father
or the Holy Spirit. In the same way we should think also of the dove which the
Person of the Holy Spirit adopted and of the voice which the Person of the
Father adopted; also the fiery tongues on the Day of Pentecost, in which the
Person of the Holy Spirit was revealed; also the wind and whatever else is
preached in Christendom or in Holy Scripture about the operation of the Holy
Spirit.
"Here one might reasonably ask: Why, then, do we say, or rather, why
does Holy Scripture teach us to say: "I believe in God the Father,
Creator of heaven and earth," and not to mention also the Son as Creator?
Also, why do we say: "I believe in Jesus Christ, who was conceived by the
Holy Ghost?" Also, why do we say that the Holy Spirit quickens us and
that He spoke by the prophets? Here the peculiar and distinctive works are
being assigned externally to each Person by way of differentiation. This is
perhaps too subtle too for simple Christians who want to adhere to their plain
faith that God the Father, the Son, and the Holy Spirit are one God, etc.
However, it is necessary to discourse on this subject in Christendom and to
learn to understand it in order to withstand the devil and his heretics. In
the first place, it is certain that God wants to be known by us, here on earth
by faith, yonder by sight, that He is one God and yet three Persons. And
according to John 17:3, this is our everlasting life. To this end He gave us
His Word and Holy Scripture, attested with great miracles and signs. We must
learn from it. To attain that knowledge of God, it is surely necessary that He
Himself instruct us, that He reveal Himself and appear to us. By ourselves we
could not ascend into heaven and discover what God is or how His divine
essence is constituted. Well, for this purpose He employs visible elements in
His creation, as Scripture teaches us, so that we may comprehend this; for
invisible creatures do not make an impression on our senses."
Luther's Works page 15:306
"When we confess in the children's Creed: "I believe in God the
Father Almighty, Creator of heaven and earth," we do not mean to imply
that only the Person of the Father is the almighty Creator and Father. No, the
Son is likewise almighty, Creator, and Father. And the Holy Spirit is likewise
almighty, Creator, and Father. And yet there are not three almighty creators
and fathers but only one almighty Creator and Father of heaven and earth and
of us all. Similarly, the Father is our Savior and Redeemer, the Son is our
Savior and Redeemer, and the Holy Spirit is our Savior and Redeemer, and yet
there are not three saviors and redeemers, but only one Savior and Redeemer.
Likewise, the Father is our God, the Son is our God, and the Holy Spirit is
our God, and yet there are not three gods, but only one God. Likewise, the
Holy Ghost sanctifies Christendom, so does the Father, so does the Son, and
still there are not three sanctifiers, but only one Sanctifier, etc. "The
works of the Trinity to the outside are not divisible."
Luther's Works page 15:309