The first triad, or hierarchy, is closest to the "Godhead" or "Father" of the universe. This group consists of:
Seraphim, Spirits of Love
Cherubim, Spirits of Harmony
Thrones, Spirits of Will
"Thus when we go to sleep at night, setting forth with our Ego and astral body, leaving behind the body of our waking life, Angels, Archangels and higher spiritual Beings enter into us and animate our organs while we are outside — until we re-awaken. And what is more, as to our ether-body, even in our day-waking life we are not able to fulfill what is needed there. The Beings of the highest Hierarchy — Seraphim, Cherubim and Thrones — have to indwell this ether-body even while we are awake; they remain there always." -Rudolf Steiner, Man as a Picture of the Living Spirit, September 2, 1923. https://wn.rsarchive.org/Lectures/ManPic_index.html;mark=223,5,13#WN_mark
"But what lives outside in this way, these super-sensible activities of Archai, Archangels, and Angels, which are reflected in the waking human being in Willing, Feeling, and Thinking — these must be harmonized with the etheric and physical bodies. The physical body must be formed in such a way that it can become the organ of thought, of speech, and of movement. One sees then how the activity of the Kyriotetes, Dynamis, and Exusiai passes over into a still higher activity: that of the Thrones, who bring human Willing into accord with the physical human organism, the human metabolism and limbs.
Then we come to the Hierarchy of Cherubim, who bring the human faculty of speech into accord with its physical basis. In all that serves speech or song in the organism, or anything similar to speech — the Cherubim bring the human life of Feeling into accord with the organs of speech. And now the faculty of Thought must also have its physical organ in the human nerves and senses. It is the Seraphim who bring Thinking into accord with the nerves and senses of man. Speech, and all that is connected with it, is brought into accord with Thinking and Feeling by the Cherubim.
...From this we see how the physical human form dissolves into appearance, and behind it there stand as realities: Seraphim, Cherubim, Thrones. We are always looking into the activity of the Seraphim, Cherubim, and Thrones, when the human Ego is interwoven with its inner activity, when man in waking life moves, speaks, feels, and thinks." Rudolf Steiner, -Rudolf Steiner, The Golden Blade, 1951, The Cosmic Word and Individual Man, A Lecture given at Stuttgart on May 2, 1923 https://wn.rsarchive.org/Lectures/CosWrd_index.html;mark=831,3,11#WN_mark
"Through the co-operation of the Spirits of Will and the Spirits of Motion, the earth would be still in that form, if another activity had not come in, one which is exceptionally enduring and which expresses itself on the surface of our earth by the fact that to the Will-forces, acting in conjunction with the Spirits of Motion, was added that which we call the activity of the Spirits of Form. You may therefore imagine that these Spirits of Form, dancing as it were upon the waves, stilled the moving masses and brought them into forms; so that we have to describe the co-operative workings of three different forces.
These three forces proceed from three sorts of Beings. You see the Spirits of Form at work, their influence penetrates upwards as well as downwards, into the sphere of the Spirits of Will as well as into the sphere of the Spirits of Motion. Above them are the Spirits of Motion, below them are the Spirits of Will. That which on our earth appears externally chiefly as a fluidic element, not however our present-day water, but the old fluidic element, which was brought to rest by the Spirits of Form, — that we must look upon as the most external manifestation of the Spirits of Will or Thrones. But another element always mingles itself with this activity. The Spirits of Will or Thrones are assisted, so to speak, by the Cherubim and Seraphim.
The Cherubim help in the element of air, in everything which permeates the apparent earthy substance as gaseous substance. Air is as it were an illusion, behind which there are the mighty Beings we call the Cherubim. The Seraphim work in what we know as heat, they are behind every sort of heat." Rudolf Steiner, The Mission of the Individual Folk-Souls, Lecture 5, June 11, 1910.
-Rudolf Steiner Archive Search on "Spirits of Form" Keyword: https://wn.rsarchive.org/Lectures/search=mode?query=Seraphim&mode=context