I know I'm coming to this discussion after it appears to have died a death, but I had to answer this question to my former Anglican parish priest when I told him I would be baptised into Orthodoxy and he questioned the status of my Anglican "baptism".
I don't put this forward as the Church's teaching but merely as my understanding of it. I don't know whether it will be of help.
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You asked about my having to be baptised. It's all tied in to the reasons I converted, really, which is why it wasn't difficult for me to accept, but here it is. Before I do go on though, I'm always wary of explaining this and related issues, as I'm very aware of the offence that can be caused. It isn't my intention to offend at all, but I would find it difficult to express this honestly without being frank. One thing that I've discovered is that, in Orthodoxy, words like "heretic" and "schismatic" are used in a very matter-of-fact way, with no pejorative associations at all. One priest will refer to his RC counterpart as a heretic, and then they'd happily go out for a drink afterwards.
I could waffle on for ages (and probably shall anyway), but this probably best sums up the Orthodox understanding of the Church.
The Orthodox understanding is very much that it is the Church, and it embraces the traditional and Patristic understanding that the Church is united in Truth, and that the adoption of beliefs different from that of the Church does not constitute the formation of a different branch within the Church, but rather a separation from the Church, as the Truth which formed the basis of unity has been compromised.
Therefore, the Orthodox Church accepts no form of the branch theory, and, in 1983, the Russian Orthodox Church Abroad (my jurisdiction) pronounced this anathema against ecumenism:
Those who attack the Church of Christ by teaching that Christ's Church is divided into so-called "branches" which differ in doctrine and way of life, or that the Church does not exist visibly, but will be formed in the future when all "branches" or sects or denominations, and even religions will be united into one body; and who do not distinguish the priesthood and mysteries of the Church from those of the heretics, but say that the baptism and eucharist of heretics is effectual for salvation; therefore, to those who knowingly have communion with these aforementioned heretics or who advocate, disseminate, or defend their new heresy of Ecumenism under the pretext of brotherly love or the supposed unification of separated Christians, Anathema!
Harsh words, I know.
Even though some Orthodox jurisdictions are members of ecumenical organisations, such as the World Council of Churches, they make it clear that this is not to be construed as recognition of other members as part of the Church, and there have been objections many times from Orthodox member churches to statements of the WCC which reflect what they call a "protestant ecclesiology". The Russian Church Abroad used to be involved in inter-confessional gatherings, and issued a statement in 1931 explaining its involvement. The Patriarchate of Moscow is still a member of the WCC and reaffirmed the Church' Abroad's statement as recently as last year:
Preserving faith in the One, Holy, Universal and Apostolic Church, the Synod of Bishops affirms that the Church never divided itself. The question lies only in who belongs to her and who does not. At the same time, the Synod of Bishops fervently welcomes all attempts of the heterodox to study Christ's teaching on the Church in the hope that through this study, especially with the participation of representatives of the Holy Orthodox Church, they will ultimately come to the conclusion that the Orthodox Church, as the pillar and ground of the truth (1 Timothy 3:15), fully and without error preserved the teaching handed down by Christ the Saviour to His disciples.
So that's Orthodox ecclesiology in a nutshell.
Regarding what that means with regards to Sacraments outside the Church (such as my baptism in the CofE), I'll try my best to explain that here.
As I've come to understand it, from the Orthodox perspective, there is no concept of sacramental "validity" as something that can exist separately from the Church, which, in the Orthodox understanding is the Orthodox church. Orthodoxy has an understanding more akin to what I would perhaps call "completion", for which the context of the fullness of the Orthodox Faith is necessary, among other things. So, for example, a recognised baptism is one that is done using the Trinitarian formula, in water, within the context of the Orthodox Church. I don't know of any Orthodox person who would say that, outside of that, there is certainly no baptismal grace, for God bestows his grace where and how he pleases. God has bound salvation to his Church, but he himself is not bound by his Church. However, I would not be able to say that it is a baptism with the same certainty that I would if it were within Orthodoxy.
Because there is no concept of sacramental validity in Orthodoxy in the same way that there is in Rome, a somewhat retrospective view can be taken of these things in some cases. So if, say, the General Synod of the Church of England were to decide to take the CofE into Orthodoxy, then that which would have been considered missing from my baptism in the CofE (fullness of Orthodox Faith) would be seen as having been restored, and there would be no need for me to be baptised upon converting.
In the 1930s, a few of the Orthodox jurisdictions independently set about answering the question asked of them by some bishops of the CofE about the Orthodox position on Anglican Orders. The response was much the same as with baptism, that there is nothing deficient about the Anglican rite of ordination, and so if one of the Anglican churches were to be received wholesale into Orthodoxy, sacramental economy could be extended so that its priests would be considered to be properly ordained, as the Orthodox Faith would have been supplied where it was previously absent. (However, this would be seen as an exception and not the norm). A Greek acquaintance of mine refers to it as the "activation" of the Sacraments, which, at first, sounded quite mechanical to me, but I honestly can't think of any better way to express it in so few words.
As it stands, my CofE baptism, while not certainly condemned as devoid of grace, cannot be recognised as a baptism. Different jurisdictions have their own ways of dealing with this. Some, (such as the Russian Church Abroad), will just go ahead and baptise and chrismate me, leaving aside questions of doubt about what went before. Others, (such as the Antiochians) would extend "economy" and so would only chrismate me, as it is both baptism and chrismation together which are seen as initiatory, and the chrismation within the Orthodox Faith would be seen as supplementing the Orthodox Faith that was lacking in the CofE baptism. None would recognise my CofE baptism as it stands.
Because of the Orthodox understanding of sacramental economy (which is, essentially, a departure from the norm for pastoral reasons, such as the Antiochian practice of chrismating and not baptising converts), the concept of validity and "conditional" baptism/ordination never developed as they did in Rome, as it just doesn't fit with the Orthodox understanding of how assurance of grace works. This wasn't difficult for me to accept. I do actually believe all of this.
This is the basis of what I was explaining when I came to see you before leaving the CofE, about kneeling at Mass on Sundays, and not being sure whether or not what was coming towards me was, in fact, the Body and Blood of Christ. Do I ignore it and risk turning my back on my Lord and God? Do I receive and adore and risk adoring what may be a piece of bread? I just couldn't do it anymore. I had become increasingly convinced by the Orthodox position for some time, and it reached a peak this time last year. I began to explore the Scriptural basis for the Orthodox position, that Christ prayed that we may all be one, and that he promised the Spirit of Truth which will lead the Church into all Truth. He prayed for unity but promised Truth, and so a departure from that Truth could not, in my understanding, be considered anything but a departure from the Church. I began to explore the Fathers and what they had to say, and they all seemed to say the same thing. The Oecumenical Councils pronounced anathemas against the Arians and those who denied the Incarnation. They were not seen as a different branch within the one Church but were seen as having separated themselves from the Church by rejecting the Church's beliefs. The branch theory began to make less and less sense as I found myself in a church which had separated from a church (RCism), which itself had separated itself from Orthodoxy, and I just couldn't justify it to myself anymore.
Because of all this, I really had very little difficulty in accepting the Orthodox position about my CofE baptism as it just fitted with my other doubts. And so here I am, knocking at Orthodoxy's door, and waiting to be let in.
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I hope this helps.
