Julian of Norwich 3

text often prefers an abstraction to a concrete term, and the word she translates here as "instant" is in Julian's text "poynte," so a more powerful translation of this passage comes from a translator of a previous Penguin edition, it goes: "I saw the whole Godhead concentrated as it were in a single point, and thereby I learnt that he is in all things."
This image is the closest Julian comes to expressing an experience of mystical union. In fact, it is not an experience of mystical union: She still views this "point" from an objective standpoint, indicating there's a duality - herself, and the fact of God's allness. She does not experience herself as God or as all her surroundings, so this is not (in Dupre's terms) "a union with a transcendent reality" nor (in Stace's terms) an introvertive or an extrovertive mystical experience.
But it's definitely mystical in the sense that it expresses an understanding of mystical reality that is revealed to her in a "state of consciousness that surpasses ordinary reality." Julian seems squarely in the phase of Illumination described by Evelyn Underhill. This is a way of saying not only that Julian does not experience mystical union, but that she accordingly never attains to the Unitive Life, which few living people do. At the bottom of p. 47 in our text a passage appears which expresses her understanding - not her experience - of this mystical fact. I am quoting the alternate translation because I think it expresses the sensibility more clearly for us than your text, you can follow it roughly:

No soul can rest until it is detached from all creation. When it is deliberately so detached for love of him who is all, then only can it experience spiritual rest. (Clifton Wolters trans., p. 68)

Without experiencing unity, Julian understands it.
A great deal of her text is devoted to talking about her understanding that the unity of everything inheres in God's love. This is a fundamental mystical idea: Socrates demonstrates it in the Symposium, and Rumi with his characteristic ability to crystallize profound thought in delightfully simple imagery says (in Coleman Barks's translation), "Your love of many different things proves they're one."
An example early in Julian's text is again in her introductory comments to Chapter 5, where she says of the spiritual, or Intellectual dimension of the hazel-nut ball vision that God "is everything that is good for us." This echoes, probably unbeknownst to Julian, the Neoplatonic identification of the Good with the One, or Absolute all. In the same chapter she indicates that everything owes its existence to God's love. In Chapter 9 she reiterates this understanding.
In Chapter 52 (p. 127) she expresses the perennial understanding that love actually binds the lower and higher worlds together - that the physical world and the divine world are in fact one because they are both encompassed or contained in love:

� the life and the virtue which we have on the lower level comes from the higher, and it comes down to us from our natural self-love through grace. Nothing comes between the first and the second, for all is one love, and this one blessed love now works doubly in us; for on the lower level there are pains and passions, sorrows and pities, mercies and forgiveness, and many similar benefits; but on the higher level there are none of these, but all one great love and wonderful joy, and in the wonderful joy there is great compensation for all suffering. And in this our good Lord showed not only our forgiveness, but also the glorious height to which he will bring us, turning all our guilt into endless glory.

Her sentence "all is one love" is a classic, simple expression of the classic mystical understanding; and in the alternate text the same sentence is given as "The same single love pervades all" (Wolters, trans., p. 124), which with a slightly different angle says the same thing, which is that love binds all the universe.
In Chapter 53 (p. 129) the same idea is expressed again when she says, "in this eternal love man's soul is kept whole," and developing the idea further in Chapter 54 she says (at p. 130):

I saw no difference between God and our essential being, it seemed to be all God � We are enclosed in the Father, and we are enclosed in the Son, and we are enclosed in the Holy Ghost; and the Father is enclosed in us, and the Son is enclosed in us, and the Holy Ghost is enclosed in us: almighty, all wisdom, all goodness, one God, one Lord.

And in Chapter 65 (p. 150) another facet of this idea is expressed when she says: "the love of God unites us to such an extent that when we are truly aware of it, no man can separate himself from another." The mystical sensibility that all people are actually one person, which occurs in all the mystical traditions I know of, takes on its Christian tint when she goes on to say, "So our soul ought to think that all that God has done was done for it." The meaning here is that God took on life at the "lower level" when Jesus was born, and that the sufferings of Jesus were given as atonement for the "sin" or separation from God which human beings willfully took upon themselves; Jesus' work, which was an act of love, treated all human beings as they are in reality - one.
To sum up, the point here is that Julian is not speculating about this, or repeating what she has heard from church teachings, or trying to invent a new Christian metaphysic. Instead, she is reporting a personal experience and trying to articulate what she understood of the experience - in other words, she is reporting a classic mystical experience, in which she gained a new sense of reality, feelings of blessedness and love, and a feeling that what she apprehended is divine. The intensity of the experience changed her inner life, as far as anyone can tell, and her expression of it matches not only the terms and ideas, but also the intensity of expression of other mystics. She experienced all three kinds of visions spoken of by Augustine, Aquinas and others, but she did not experience mystical union in the way W.T. Stace and others define that experience. Julian's experience occupies a stage of personal growth indicated by Evelyn Underhill's description of Illumination, at an intense moment (or point) between the stage of Purgation and the Unitive Life, before the final struggle Underhill called the Dark Night of the Soul.

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References
Julian of Norwich. Revelations of Divine Love. Elizabeth Spearing, translator. Penguin Books, 1998.
Julian of Norwich. Revelations of Divine Love. Clifton Wolters, translator. Penguin Books, 1966.
W.T. Stace, Mysticism and Philosophy, MacMillan, 1960.
Evelyn Underhill, Mysticism: A Study in the Nature and Development of Man's Spiritual Consciousness, E.P. Dutton, 1961.