What is The New Church?

One result of that slide was that direct revelation from God to everyone was no longer possible and was given only to chosen individuals.  By means of those revelations, God gave, in later ages, the Ancient Word (at the time of the Ancient Church) and then the books that were put together as the Old and New Testaments, at the times of the Israelitish and Christian churches.  (The first 11 chapters of the Old Testament were copied by Moses verbatim from the Ancient Word, actually, which is why those chapters are stylistically different from the rest of the Old Testament. The rest of the Ancient Word, which included the books of Jasher and The Wars of the Lord referred to elsewhere in the Old Testament (Joshua 10:11, 2 Samuel 1: 18, Numbers 21:14,15), is now lost, though perhaps not irretrievably.)

The reason for the repeated revelations was that, after each one, people would, after a while, begin to distort and misuse the teachings of the revelation, just as they had chosen to leave the paradise state of the Golden Age.  However, God plays fair and keeps supporting free will.  That meant that every time people got into evil and did this distortion and misuse of His teachings, he provided a new revelation to clear up the false interpretations and confusion that resulted from these distortions and misuse.  The new revelations did not replace the previous ones but provided new insight into them, which, for instance, Jesus Christ referred to as "fulfilling" (Matthew 5: 17) earlier teaching.  Part of this process, as noted in "The human race has grown up intellectually. So have God's explanations," was that each new revelation provided more a more intellectually "grown up" explanation of spiritual truth than the previous one. 

Just as growth stops when we reach adulthood, so, the Writings teach, the truths contained in them are the final revelation, providing the full "grown up" explanation spiritual truth that has not been available to the human race since the Golden Age.  That, of course, is an extraordinary claim and two things should be noted with respect to it.  One is that the Writings  claim to be only part of the "full story" - the divinely inspired books of the Bible remain the fundamental part of that "story," and, indeed, much of the Doctrines consists of further and deeper "fulfilling" explanations of Bible truths.  The second point is that the Doctrines reveal the key to Bible symbolism, and to the symbolism of creation itself, that has been lost since the Golden Age.  Called the doctrine of "correspondences," it provides a whole huge realm of investigation all by itself.  When the Bible, the Writings and the perspectives opened up by the doctrine of correspondences are taken together then, there is more truth involved than anyone could learn in a lifetime.  It is thus understandable how, right at this practical level,  this could in fact be the final revelation.

Coming back to the original question, "What is the New Church?", then, the New Church is two things:  At the spiritual level, it is comprised of all the people who truly believe and live its teachings.  The membership of this "internal" church is known only to God.  At the external level, in this world, the New Church is all the people who are trying to follow the teachings of the Writings, some of them in organizations, some as individuals on their own.  As noted in "Is the New Church like other church organizations?", even when there are church organizations, they are pretty low-key, since the emphasis is always on free will and the individual's relation to God.