A trad Roman Catholic follower of mine on Twitter asked me to compose my own version of this list of 10 things Protestants should know about Orthodoxy, since I had commented that my own list would be quite different. While Dunn's list is pithy and lighthearted, mine is somewhat more self-serious. I'm sure there are similar lists out there written by more knowledgeable people, and these points will be quick glosses of subjects which could be expounded upon in great length, but here is my list.
Holy Tradition is how the faith is passed on. The Bible is not the sole criterion of the faith, rather it is one aspect -- though an especially glorious, radiant, central, and exalted aspect -- of Holy Tradition. The Church, the Body of Christ, is a living organism and her faith is a living faith. The Holy Spirit is not only operative and authoritative within the Church when the Apostles were putting pen to papyrus, but also when they taught by their word (2 Thess. 2:15), when they convened councils to make decisions on controversial matters in the Church (Acts 15), when they are passing on their authority to others (1 Tim. 4:14; Acts 6:2-6), and when they decided on the canon of Scripture. The New Testament is the written expression of apostolic tradition, and as such is authoritative as an extension of the authority of the Church which Christ established (Matt. 16:18-19). But this authority can never be divorced from the Church, and the Bible is true and authoritative to the extent that the Church wrote, canonized, interprets, and teaches it. These functions are integrally related, which is why you can't take one of them (the canon, for example), and divorce it from its source and life, which is the Church.
Because the following is true, Ecumenical councils and their canons are received as authoritative and binding on the whole Church (though their application is left to the Bishops). This is also why the Nicene-Constantinopolitan Creed is the definitive statement of Faith of the Orthodox Church, being the product of the First and Second Ecumenical Councils.
Salvation is not a juridical imputation of Christ's righteousness which transpires the moment one first 'believes'. Certainly Christ's incarnation, death, resurrection, and ascension are our salvation, and it is only by Christ's gracious acts in history that salvation is possible. Without Christ we would be dead in our sins and without hope. And it is through faith that we receive His grace, but faith is not mere intellectual assent, it's also faithfulness; living in accordance with that faith in the Church. Individuals can truly respond to the free gift of salvation that Christ offers, or reject it. Responding means an ongoing process of being saved, and being saved means union with Christ in his Church through the sacraments and by the Holy Spirit. The Orthodox Church calls this process theosis. We are called to become "partakers of the divine nature", in the words of St. Peter. With this being the case, there is no 'assurance of salvation', and instead we are called to "work out our salvation with fear and trembling" (Phil. 2:12).
The Orthodox Church is highly sacramental. The sacraments of the Church are the mysteries of Christ through which his grace is made incarnate in the Church by the Holy Spirit. The grace of Christ is offered freely to all through his Church, and the sacraments are the means by which it comes to us. In Baptism, the priest calls the Holy Spirit down onto the waters and we mystically join in Christ's death and resurrection, putting off the old man, being grafted into the Body of Christ, and thereby being made into new creatures. The change that is effected is not merely an outward sign of an inward change of heart, but it is in the waters of the font that an actual, real ontological change is affected. This is why it's necessary that we are baptized (John 3:5), and it's true that baptism actually removes our sins (Acts 2:38). The Eucharist is the body and blood of our Lord (Matt. 26:26-28; John 6; 1 Cor. 11:27-29), given for the healing of soul and body and the binding together and sustaining of the Church. The Orthodox Church recognizes 7 'official' sacraments (Baptism, Chrismation, Holy Communion, Holy Orders, Confession, Marriage, Holy Unction), though it doesn't teach that sacramentality is confined to these things.
The Orthodox Church is the "one, holy, catholic and apostolic church" referred to in the Nicene creed. It is the Church that Christ founded. The authority that Christ gave to the Apostles is passed down by apostolic succession within the Church -- that is by the laying on of hands to the successors of the Apostles, the Bishops. The Orthodox Church has uniquely and exclusively maintained apostolic succession and fidelity to the faith as handed down by Christ and the apostles, without addition or subtraction. Orthodoxy rejects the innovative 'branch theory' of ecclesiology which holds that the Church is invisible. In the first millenia of the Church, there were no 'denominations': there was the Church and schismatic sects who willfully departed from the Church. St. Paul writes that there "must be heresies among you" so that the truth can manifest itself (1 Cor. 11:19). And so it is today. The Orthodox Church also rejects Roman ecclesiology (as it developed and came to a head in the 11th century) which holds that the pope is the head of the Church, with a special claim to authority over the other bishops. The head of the Church is Christ and all the bishops share equally in the apostolic inheritance, despite the bishop of Rome's exalted place of honor in the early church.
The Orthodox Church teaches that the faith was delivered "once for all to the Saints" (Jude 1:3) and that "Jesus Christ is the same today, yesterday, and forever" (Heb 13:8). As such, Orthodoxy rejects in principle innovations in doctrine, praxis, or worship as deviations from Holy Tradition. If it's new, it can't be true. Various small-t traditions -- some good, some neutral, some bad -- obviously exist within every local church and differ from culture to culture and age to age. It's important to distinguish these variable traditions of men which exist in the church from infallible Holy Tradition, the Tradition of God. Guidance for such discernment is provided by the teachings of the Church.
Bishops are the recipients of the fullness of Apostolic authority. They are the locus of authority in the Church, and a priest's authority is derivative of that of the bishop. Not everyone who hears the Gospel preached and responds positively thereby becomes an authority on the things of Christ and the Church. We don't see this in the New Testament. This is uniquely the ministry of the priesthood. Just as Christ chose twelve to be his disciples, so his chosen and set-apart disciples choose and ordain those who are to receive the apostolic ministry of the priesthood. However, this authority is also subject to what is called 'conciliarity', meaning lay people have a role in receiving decisions of bishops as in accordance with the rule of faith. The 'amen' of the people is a necessary element, as this prevents rogue councils of bishops from legitimizing heresy, for example.
Because the Church possesses the mysteries of Christ by the Holy Spirit, and its teachings are therefore authoritative, the proper disposition of any member of the Church -- lay person, deacon, monastic, or bishop -- is one of humble obedience. If the Church teaches something that you don't agree with, then it's incumbent upon you to acknowledge that you are wrong, give up your personal opinion and submit to the authority of the Church.
Asceticism -- persistent repentance, prayer, fasting, labor (physical and spiritual), self-denial and obedience etc. -- is the authentic mode of Christian spiritual life, and not something that is "just for monastics" or -- a much worse slander -- not Christian at all. It is the means by which we enter into the life of Christ and partake of his suffering, taking up our cross daily and denying ourselves. We're called to not only thankfully receive suffering and hardship as it comes to us as a means for our own growth and upbuilding (though we are so called), but also to willfully search out and walk the path of the cross, which is the path of Christ. The pitfalls along this path -- such as empty outward performance without true inward contrition and humility, or haughty self-righteousness -- are perilous indeed, but it is in walking this path that we are forced to confront such temptations and, by God's grace and our own struggle, overcome them to our own sanctification and the benefit of all we come in contact with.
Those who are able to devote themselves most fully to a Christian life of asceticism are the monastics, who have a special place in the life of the Church. They devote themselves to prayer for the world, to living a life of obedience and self-abjection for Christ's sake, and it is from their ranks that many of our bishops come from. Monasteries also have an important relationship in maintaining standards for the whole church, which laity look to for inspiration, edification, and example.
The worship of the Orthodox Church is liturgical. As with matters of doctrine and morality, how we worship is extremely important and is authoritatively passed down within the Church. Indeed, it is in the services of the Church that theology is actually done. Lex credendi lex orandi. The hymnography, prayers, iconography, liturgical calendar, and architecture of the church all work together to express the truths of -- and draw us into the life of -- the Holy Trinity. The form of worship is closely and intimately bound up with the 'content' of it, and loosing standards on the form inevitably affects content. Examining those traditions where worship is not done in accordance with Church tradition always reveals a corresponding 'loosing' of standards elsewhere -- doctrinally and morally, for example. But such practical concerns are not the main reason for liturgical worship, rather it's because liturgical worship is of apostolic provenance, and the Church is One -- the Saints (and the angels) in heaven worship with us in one accord, and we worship with them. And so we worship how the Saints worshiped when they were alive on earth.
9) Veneration vs. Worship.
In the Orthodox Church we venerate. We venerate the cross, the Holy Icons, the Holy Gospel, the relics of Saints and other things. Veneration (ghoulia in Greek) is not worship (latreia in Greek), which is reserved for God alone. We venerate Holy items because, as St. John of Damascus says, "I do not worship matter; I worship the Creator of matter who became matter for my sake, who willed to take His abode in matter; who worked out my salvation through matter. Never will I cease honoring the matter which wrought my salvation!"
10) The Theotokos and All the Saints.
The Theotokos -- Mary the Ever-Blessed, Most Pure, and Mother of Our God -- has an exalted place in the Orthodox Church. She is the first of all the Saints, and we ask for her Holy intercessions more frequently than any other Saint, and also venerate her in accordance with scripture (Luke 1:48). This is because God found her worthy to be His Mother, and she submitted to His will. Her powerful intercessions are evident in the Gospels as it is through them that Christ performs His first miracle. He tells her it's not the time to do his first miracle, yet when his mother effectively insists, He goes on to perform it anyway (John 2:1-10). If Christ honors His Mother -- and even obeys her! -- shouldn't we do the same? And shouldn't we desire her miraculous intercessions on our behalf? We pray to the Theotokos and the Saints because God is the God of the living not the dead (Matt. 22:32; Mark 12:27), and the Saints are alive in Christ. With this being the case, we turn to them for prayer first and foremost because "prayer of a righteous man availeth much" (James 5:16).
The Saints also edify us through their lives and their writings, by being examples of how to live a Christian life, and a testimony to the authentic reality of the experience of God in the Church. Because the Church isn't a fossilized object waiting to be exhumed, but is a living organism, new Saints are always being made and nourishing the Church with the wisdom of the Holy Fathers. But whether it's a living Saint or a Saint in heaven who we come into contact with through the Tradition of the Church, we should look to them as examples and submit to the wisdom of those who have beheld the true light of Christ.
For a trad Roman Catholic, much of this will be familiar. My list of 10 things Catholics should know about Orthodoxy would be somewhat different, on the Orthodox view of issues like the filioque, the papacy, liturgical theology, modernism, divine essence and energies as opposed to 'created grace', etc. But, being that I come from a Protestant background and not a Roman Catholic one, those are things I'm also much less equipped to comment on in an illuminating manner.
Much more could be said on each of the above points, so please forgive any imprecision or mistakes. If anything in the above list is wrong, which is entirely possible, please correct me.