I've been reading quite a bit of early church history of late, particularly that history which surrounds Marcion. For those unfamiliar with him, sources tell us he was a Christian who made considerable money in the shipping industry (he lived on the coast of the Black Sea), and decided to give that up for some kind of career in missions. He moved to Rome and made a sizeable donation to the church there, before gaining an audience with some of the church leaders, during which he shared his opinions on matters theological.
Here is where it all went wrong for Marcion. His opinions (a word which comes close to the meaning of "heresy") were not well received. His donation was returned to him, and he left the church in Rome in order to forge his own path; indeed, his own church. From what we can gather, the Marcionite church was a serious rival to the proto-orthodox Church, and there is evidence to suggest it lasted right up until the tenth century.
I must confess, I have sympathy for Marcion. I have done for quite some time. That is not to say I agree with his opinions, or with his methods. Marcion was convinced that the Old Testament God was different to the God revealed by Jesus. The Old Testament God, so his story went, was a God of pure righteousness. He was not an evil God. He was simply legalistic to a fault. The Father to whom Jesus referred, however, was a God of love, of forgiveness, of peace. He was the unknown God who suddenly became known through the Christian gospel. For Marcion, then, the Old Testament was not a foreshadowing of Christ but the antithesis to Christ.
In fact, Marcion's major work (which is lost to us) was titled Antithesis. In it he contrasted the Old with the New. For example, in the Old, the sun is stopped so that Joshua could slay his enemies; in the New, Christ tells us not to let the sun go down on our anger. And, in the Old, the prophet Moses stretches out his hand so that many will be killed in war; in the New, the prophet Christ's hands are stretched out on the cross so that many will be saved.
As I said, the church rejected Marcion's notion of there being two Gods, and continued to believe that the Scriptures of the Jews belonged also to Christianity; in many cases, in fact, that the Scriptures of the Jews belonged exclusively to Christianity, since by their rejection of Jesus as Messiah the Jews forfeited their claim on the Scriptures.
There were (and are) good reasons for the Church to affirm the continuity between Old and New. Marcion could only avoid these reasons by writing off three of our four gospels as corrupt and heavily editing the gospel of Luke, ridding it of what he deemed Jewish interpolations. Along with Luke's gospel Marcion included ten of Paul's letters in his canon of Scripture. For Marcion, Paul was the only faithful apostle, since the apostle to the Gentiles was the only one who discerned the radical newness of Christianity, a newness which made a clean break with the past.
Marcion, it should be noted, was not necessarily anti-Semitic; or, at least, he was no more anti-Semitic than his orthodox opponents, and perhaps a good deal less. His issue was that he was unable to reconcile the gospel of Christ with the Old Testament. As the title of his work indicates, he could only see contradiction between the two. Here is where my sympathies with Marcion lie. I think the Old Testament is far more a problem for Christians than is generally acknowledged. One only has to go through the lectionary and notice what is not included in order to discover the unacknowledged problems that the Old Testament throws up for the Church. Our canon includes the Old Testament (though even here, this is no agreement regarding the books which comprise the OT), but I do not think we use it as a measure. Rather, our use of the Old Testament reveals that something else is measuring the Old Testament, something which dictates that certain portions of it are ignored. At this point the Church is more or less Marcionite in its practice, without fully subscribing to all that Marcion believed.
There is a good reason why the Church has adopted a subtle form of Marcion's techniques. Marcion, like most interpreters today, found no use for allegory. He read the Old Testament at face value, and in much of it he could find nothing of edification. One of the reasons the early Church was able to adopt the Old Testament as its Scripture was precisely because the Church's interpreters had the method of allegory in their hermeneutical arsenal. The early Church was not oblivious to the problems which Marcion raised. Rather, through the method of allegory, the Church was able to find use for those passages which Marcion rejected. Nowadays, however, this option is more or less unavailable to us (though there have been recent attempts to revive allegorical interpretation of the Old Testament - for example, Douglas Earl's work on Joshua).
I may be overstating the case, but it is not wholly unreasonable to claim that the early Church was Marcionite when the Old Testament was approached literally. Only when the text could be approached using a different sense was the Church able to avoid Marcion's ideas. But where does that leave us today, we who are the heirs of literalists?