Friends, the following is from the modern Orthodox
theologian Fr Dumitru Staniloae, a brilliant theologian and a
confessor of the 20th century, who was imprisoned under the
communists in Romania for several years. This is from his
Dogmatic Theology, volume 5, pp29-31.
Through His Incarnation the Word of God has introduced the Holy Spirit once again, and to the highest degree, into communion with creation. By bringing Himself hypostatically within the framework of creation by taking our flesh upon Himself, or rather, by making Himself the very hypostasis of creation, the Logos brings the Holy Spirit as hypostasis into His humanity and, through it, into creation. From this point onward, the human being who opens himself to Christ through faith can be born again through the all-powerful activity of the Spirit. To this end it was necessary for the Spirit to take part anew and in an incomparable way - as He did not participate even at the creation of Adam - in the birth of the Son of God as man, the birth of the New Man.
In this way nature has been freed from the chains of the rigidity of natural laws and from the inexorability of an eternal death, and also from the power of demonic forces, a power that contributes to this bondage of the freedom of the human spirit and that in the end leads to the death of spirit and body alike. The restoration of the free image of the divine Logos in the human being has been brought about in its fullness by the Logos Himself, who, as hypostasis, takes to Himself - with the cooperation of the Holy Spirit - this image that is His very own. The Spirit extends Himself too, through baptism, into those human beings who believe in Christ, and refashions the image of the Logos within them.
Because human beings were not able to pass over to this new life because their own lives came to an end, they could not return to it except through another birth, one in which the Holy Spirit, the principal factor in this rebirth, would also render intensely spiritual, through baptism, the liquid reservoir of the universe. Although the incarnate Son of God had no need of such rebirth through baptism, for He was born of the Spirit from the beginning, He accepted baptism for our sake so that, in this regard as well, He might be the first human being to be baptized in water and the Spirit. By doing so, in a concrete way He united the Spirit within Him to the water, as womb and sustainer of life, a life now no longer subjected to death because of its complete union with the Spirit. In this way Christ "fulfill[ed] all righteousness" (Matt 3:15), the righteousness with which He was to clothe anew all those who put their faith in Him. He accepted both of these acts in succession because we have to pass through both ourselves. For this reason, the Fathers see baptism as based in both the birth and the baptism of the Lord. The baptismal font is for them an image both of the womb of the Mother of the Lord and of the River Jordan.
At Christ's baptism, the Holy Spirit unites Himself again, for the sake of Christ, to water and to the whole of creation, which is so intimately connected to Him.
Man is thus reborn as much from Spirit as from cosmic matter, inasmuch as the water represents this matter in a liquid state, as a reservoir and womb for every form of organized existence. Baptism has a cosmic significance. It means that matter itself, brought back to the condition of spiritual mobility, becomes a milieu for the creator Spirit, who is free and ever new in all His acts. The water of baptism is, in a hidden way, the matter of the age to come that will bear within itself the Son as resplendent hypostasis and the Spirit with His life-giving and ever-new energies. But this water has now been made spiritual for the sake of human rebirth and the reestablishment of humanity's relationship with God. The fullness of this spiritualization of water will only be made visible, however, in the age to come, for the purpose of bringing to fulfillment humanity's relationship with God, and this is when that water which was created at the beginning, as a means of developing the relationship between human beings and God, will be shown forth in its final state.
When a man is immersed in this water at baptism, he encounters Christ within it, or he is enhypostatized in Christ; he is fully personalized within the Person of Christ and is filled by the energies of the Holy Spirit that shine forth from Christ. The Son had to be immersed in human nature and, through that nature, in water, so that we, by immersing ourselves in water, can be immersed in His divine life, in His Holy Spirit.