"The prayers of the chrismation service speak of grace - the grace of the gift of the Holy Spirit - as a reminder that when we enter into the life of God through baptism and chrismation, we are totally and obviously on the receiving end of God's love. All we need do is to be present. God promises to do all the rest. No one can be naturally worthy of baptism or chrismation - it is a free gift, and the only possible authentic response is grateful acceptance."
One of the strongest pieces of symbolism with chrismation is that of being 'marked'. Marked for the Kingdom. Marking a person is a powerful biblical image, beginning with Cain and Abel and continuing right on through the Book of Revelation. Markings are made so that people or objects can be known. Cain's marking was to let people know to leave him alone, rather than seek revenge for Abel's killing. His 'therapy', his opportunity for repentance, was to remain alive, rather than lose himself to death. The story of Cain and Abel (especially the marking of Cain), is misunderstood quite often. What it actually does is serve to underline the fact that the spiritual path is open to everyone at any time, no matter how bad they are or how bad they *think* they are. However, the path is not an easy one, and there's always work to be done while on it.
The mark of chrismation is invisible and indelible. No matter how badly we perform, no matter what struggles we have, we are marked for God, and we are marked for life.
Being 'in communion' is more than just the ability to receive Holy Communion together. It's a sense of place and belonging, of common thought and belief and purpose. This is shared throughout the Church, both those members on earth, and those who have passed from this life. Death is no barrier to being in communion.
"Thus the sense of belonging, an adoption of an essential identity, is paramount in the way in which the Orthodox Church sees herself. This provides the human personality with great comfort in a world often seen to be hostile, projecting a clear sense of alienation. The gift of the Holy Spirit, the dynamic spiritual movement, gives the person a sense of belonging that the world is unable to eradicate."
The second aspect of the mark is that we become inheritors of the gifts of the Spirit. In place of fear and greed, we are presented with generosity and confidence. In place of insecurity and alienation, we are firmly given a sense of belonging and identity.
And finally, we are 'sealed'. We are made 'special' (though God makes us all equally special), and reserved for God.
He does, in the last section, cover the fact that adults can convert to the Orthodox Church through means of chrismation alone. He doesn't go into much detail, but the impression I get is that it works similar to how it does in the Catholic Church. Once baptized properly (Trinitarian formulae), one cannot be baptised again. So for those who come from a tradition that practices proper baptism, they are chrismated, but not baptised.