, with all due respect and speaking as an ex-Seventh Day Baptist (SDB), if you were a Fundamentalist who converted to the Charismatic movement then you have never been a Christian. Let me compare it this way, if a Samaritan living 2000 years ago became an Essene, he could not rightly claim to be an Israelite even though he had been part of two movements which thought they were Israelites. (Please forgive any error in this comparrison.) The point is that neither the Fundamentalist nor the Charismatic movement is Apostolic and as such neither can rightly claim to be Christian.
(You can probably figure out a thing or two about SDBs simply from the name of the group however individuals vary widely and wildly within the movement as it encompasses all ranges of Baptist thought with the uniting point being the Sabbath. Only Primative SDBs are of note as not being part of the main SDB body as far as I am aware
although smaller groups exists. The PSDBs as all PBs don't believe in such organisations.)
May I please ask how recently your friend converted to Orthodoxy please?
From what you have said it is clear that you do not accept the Holy Bible as being the infallible Word of God. However it is interesting that you mention God as most Buddhists are either atheists or polytheists.
You talked about Testimonies, if you haven't read it and would like to, I recommend Thirsting for God in a Land of Shallow Wells by Gallatin (not sure of how to spell his name sorry but that's close).
Your friend is probably concerned about you as the Church is like Noah's Ark. If you're not in it then you have no hope according to strict Orthodox teaching. Note please though, the Orthodox Church knows who is in the Church but not who is out of it. God gave the Church one way of ensuring people are in it but if God has another way then He didn't tell us about it. Hence, the safe way is considered the best way.
In regards to the "we are the one true church" mentality that you mention, if it is used to exalt oneself or degrade others then this is sad. However in Orthodoxy it is simply put forward as a statement of truth that Christ said, I will establish my Church and the gates of Hell (Hades) will not prevail against it. The Holy Bible also strictly warns against separating from the Church which the Apostles founded. As the Orthodox Church is this same Church it is simply stated as fact that the Orthodox Church is the one true Church and then if you don't want to accept that then it won't be pushed. Whilst without the Church you are free to believe whatever you like and the Orthodox respect the right of a man to be wrong.
May I please point out that the Muslim who flies an aeroplane into a building feels close to God. How one feels is no indication of reality. If I eat magic mushrooms I might feel great but my health won't be so great. If I feel that I know a lot about the Holy Bible as an SDB, this just means I haven't yet been involved with people (such as the Orthodox) who know a lot more than I do.
Please be specific about what things people believe about Jesus Christ which He did not say about Himself. Remember also that not all His words are in the Holy Bible as St. John tells us and that He taught His Apostles many other things which have been received by the Church.
There are some things which are unknown. For example, what happens to unbaptised babies which die? Some will contend greatly for both sides of this issue which is evidence that it remains unknown but what is known is that baptised babies are safe.
The Lord Jesus Christ sent the Holy Ghost (Holy Spirit) to guide His Church into all truth and He guides the Council when it is Ecumenical. (Oriental Orthodox Christians will here contend that there have only been three  however issues regarding the next three  have been largely resolved now and OOs agree with the one about icons anyway.) As ozgeorge said, a Council has to reach a consensus and that at Chalcedon did not as about 1/3rd of the Bishops disagreed and St. Dioscorus was falsely deposed.
To clarify as well, a heretic has to know that he is wrong and be warned repeatedly before he is called a heretic. Why he is wrong is explained to him several times and any issues of difficulty are discussed but if he is to change the faith which was once delivered to the saints then he can not remain a part of it. Calling a person a heretic is the last kind act the Church shows a person in the hope that he might repent of making his own choices (which is what heresy means) against the wisdom of the Church.
In regards to the Council of Florence, I know there were Ethiopian Orthodox Christians there which did not agree with Rome however I'm unsure about any other OOs. Also, isn't Mark of Ephesus a saint amongst the EOs?
I've replied to this quickly and briefly as I am not yet baptised and so it is unlikely that anyone will listen to me however my father has been a western-style Buddhist for some years so I have some knowledge of this topic. I would like to ask please if you are aware of how different western-style Buddhism is to Buddhism as practised about the Indian sub-continent and in SE Asia and Japan?
Please forgive me for being too direct however I fail to see why I should be subtle as usual at a time when nobody will listen to me anyway.
In short though, as it was your original question, I am about to convert to Orthodoxy and become a Christian (at long last after having been through many denominations and investigated various groups even including the Strangites) because I keep seeing miracles unlike anything that I have ever seen anywhere else (and they aren't just silly "my back was sore and now it isn't" type of miracles) and it has amazed me how many attempts at investigating other religious groups have failed for one reason or another, particularly in the last few months, whilst I have been investigating Orthodox Christianity. Also, I have been reading the writings of early Christians and other works and, whereas I once debated doctrine powerfully, I am now unable to stand any longer against the teachings of Orthodoxy in debate. I must say though, I still have a question that I would like answered before joining the Church but I'm now satisfied that if I just stop tarrying and organise to be baptised the answer might be given me afterwards.
Hope you read this as I haven't read everything but generally looked at the first page.
Having just read that story, hedley
, about "Why would He change?" I must relate that to some others. Thank you for it. I might change it a bit as I'm a bit of a story-teller and prefer longer stories.
Hope that helped Buddhalover.
+May the prayers of St. Mary, the Holy Apostles, the saints of this day and St. Didymus the Blind be with us, IS.