In The Declaration of the Holy Mountain in Defence of Those who Devoutly Practise a Life of Stillness Palamas defends the theological basis of hesychasm against the criticism of its opponents. Palamas does this first by introducing the patristic basis of his theological vocabulary, and then by answering each of the criticisms in turn in six parts.
In the prologue Palamas uses the principle of the continuous revelation of God through Moses and onward to place hesychasm, and those who experience it, within the line of this revelation which will conclude in the eschaton when “it will be clear that the present mysteries accord with all that is then made manifest.” Because this revelation has made clear that the tri-hypostatic Godhead is “one simple, non-composite, uncreated” nature, when Dionysius speaks of the grace of deification as “divinity and the source of divinity and goodness” he is not speaking of two divinities. Rather, this grace proceeds eternally from God, ungenerated and completely real, as St. Maximos says. This grace has been expressed in many different ways, as light, fire, oil, etc.
Palamas then gives his first response to his critics, entering into a diatribe with a hypothetical person who has passed judgment upon the theology of hesychasm. Palamas says that to call those who believe that the deifying grace is uncreated, ungenerated, and completely real Messalians and ditheists is to excommunicate oneself from God and the saints. Palamas enters into no reasoning for this statement, depending upon his what he has already said in the prologue to make this pronouncement clear.
In the second response Palamas counters those who say that union with God can be accomplished through mere human effort and intellect through imitation of God, and in a rhetorical tour de force accusing such people of Messalianism themselves. The grace of deification, Palamas says, is unconditional, beyond human faculties of achievement. For if it could be achieved merely by human faculties then anyone could simply work themselves into being God. Obviously this is impossible for the point of deification is to be raised outside oneself, not to simply continue within ones nature.
The grace of deification, therefore, is above nature and above virtue and knowledge. Our growth in virtue can, indeed, prepare us for our union with God, but it, in and of itself, is not the basis on which deification occurs. One can suppose that such is also the case for knowledge. Palamas says the grace of deification is rather the entirety of God penetrating the saints, who then in turn penetrate God entirely, acquiring God so closely that they are in him as his own members.
Palamas then turns to the third accusation, that those who locate intellect in the heart or the head are Messalians. Palamas responds that, this again, is an attack on the saints, and quotes Athanasius and Macarius as examples of saints who located the intellect in various parts of the body. The fact that they locate it in different parts does not concern Palamas, rather the point is that they all locate it in the body, for as he quotes Gregory of Nyssa as saying, the intellect is united to the body. To make clear his point, Palamas draws an analogy from the Incarnation, showing that what is divine can be located within a place and that this does not contradict the fact that divinity is, by definition, disembodied.
In the fourth response, Palamas answers those who state that the light of Tabor was a mere apparition and not an unsurpassable reality. Palamas again states that those saying this are going against the saints, quoting from liturgical texts which do state that the light of Tabor was uncreated, infinite, eternal, and etc. Palamas says this is because the light which shone from the flesh of Christ on Tabor was an expression of the light which he always had and was, but which was invisible to everyone until “he opened their eyes so that instead of being blind they could see.” Since Christ is “the true light”, when his disciples saw him as he really was he “shone forth like the sun”, though such an expression is imperfect, for it is impossible to use words to explain that which transcends creation in creaturely words.
Fifthly, Palamas responds to those who state that only the essence of God is uncreated while the energies are created by appealing to Maximus, who lays down the principle that there are some things which have always existed. Since goodness, life, immortality, simplicity, immutability and infinity all appertain to God, non-existence was not prior to them. Such things are realities and God is the eternal author of them. Palamas makes the distinction between these things, which are without beginning, and the Triadic Unity, which is intrinsically without beginning. So, not everything that issues from God is subject to time.
Sixth and lastly, Palamas defends against those who say that hesychasm is devoid of the body, therefore seeing no purpose in pursuing virtue and the death of evil habits. Palamas appeals to the bodily resurrection to show that just as the body will share in the blessings of the soul in the age to come, so does the body share in the grace which God gives the purified intellect. Because the body and soul share a cojoint existence, as the soul is transformed and sanctified the body is also transformed and sanctified. When the soul moves towards becoming “capable of perceiving the ineffable goodness of God” the joy of the soul is also shared by the body.
Palamas explains that this shared experience is based upon the faculties of each part. The intellect and the senses experience the light based upon its ability, the intellect according to spiritual knowledge and the senses according to sight. When both perceive light it is not the same light, and when saintly persons have the grace to see with both sight and intellect they see “that which surpasses both sense and intellect.”
In this treatise, Palamas makes his apologia for hesychastic theology based upon the long history of the mystical experience in the Christian tradition. In this he is able to show that hesychasm does not cause one to become a ditheist, is not a result of human achievement, that the intellect is not separate from the body, that the energies are not created, and that the body is not superfluous to the mystical experience. In making this defense, Palamas lays the foundation for how the mystical experience is thought of in Orthodoxy, and its theological basis and reasoning.
 G.E.H. Palmer, Philip Sherrard, Kallistos Ware, trans. The Philokalia Vol. 4 (London: Faber and Faber, 1995) 418-425.