Where does it say in Scripture that one cannot leave a local assembly and go to another local assembly who are actually committed to worshiping the Lord in spirit and truth? Or are you applying loose principles?I think my principles are pretty tight.
Here's my reasoning:
Jesus Christ came to establish his kingdom among men in creation. That is: he came to do a real thing -- something you can see, feel, touch. The advent of that kingdom is the church. (and while I think doing this breeds a lazy habit in the readers, cf. Mat 16; Acts 2; 1 Cor 1; 1 Cor 12; 2 Cor 8)
When we say "the church" and mean "no such gathering in particular but any such gathering in general", we abuse the word "church" (really: ekklesia) into something which it does not mean. In almost every case in the NT, the word "church" refers to a particular gathering of the believers (see all the references above; also Gal 1; Eph 1; Eph 5; Phl 3). When "church" does not refer to the local assembly, it refers to all such bodies in order to draw from the idea of what is given to all believers to the specific matter of some local church (see 1 Cor 1; Col 1).
In this, one thing is certain: Christ loves the church -- not just in general, but specifically all local churches. That includes, for example, the church in Galatia who was believing and practicing something Paul said made the work of Christ into nothing; that includes the local church in Corinth which was divided, permissive toward sin, abusive toward the sacraments, unsure about idolatry, chaotic in worship, and forgetful of the Gospel. That is: it is unquestionable that Paul called both of these badly-corrupt bodies "churches" who still had the blessing of Christ and the cornerstone of the Gospel upon which to build or rebuild its faith life.
Now, here's where we either must follow scripture or just admit we don't intend to at all: in both these cases where the local church has pretty much done its worst, Paul does not instruct anyone to flee. That's an important "not said" -- but only because it is in direct opposition to what Paul actually said. In Galatia he did not say, "so the few of you who are right with the Gospel should abandon those who are not," but he did say, "I am afraid I may have labored over you in vain. Brothers, I entreat you, become as I am, for I also have become as you are... Have I then become your enemy by telling you the truth? [the Judaizers] make much of you, but for no good purpose. They want to shut you out, that you may make much of them. It is always good to be made much of for a good purpose, and not only when I am present with you, my little children, for whom I am again in the anguish of childbirth until Christ is formed in you! I wish I could be present with you now and change my tone, for I am perplexed about you." [Gal 4] That is, he said, "because you are in dire faith trouble, I want to come back to you." And then a moment later he says, "Now you, brothers, like Isaac, are children of promise. But just as at that time he who was born according to the flesh persecuted him who was born according to the Spirit, so also it is now." That is: "You, my brothers, are being put to a terrible test -- like Isaac being persecuted by his brothers."
Not one hint of fleeing, but a broad and clear message of staying together in the course of faith, staying the course in a time of trouble, and a longing to be with them through the hard time.
Is your church like the Galatian churches? Then do what Paul did and exhorted them to do because they were a church, and your assembly is also a church. This does not apply to Mormons, or JWs, or Hindus, or what have you: it applies to churches in the heritage of faith which have not openly dismissed the Gospel from their midst.
But a church is a church, not a commodity. It is a place where we have brothers and sisters, not merely acquaintances and buddies. The calling there is greater than marriage and greater than family -- and to treat it as lesser or inconsequential is to wholly negate what Paul here appeals to in order to win the Galatians away from their corrupted ways.
It is exactly what Dr. MacArthur says in his opening sentence: something which cannot be done lightly. It is a grave matter to leave a church -- and not a matter which we should see as merely preferential or opportunitistic.
The local church is called a body in which all the members need each other. In 1 Cor 12, Paul makes the case for many gifts and many kinds of members to dispel the Corinthian enthuisiasm for the ecstatic gifts -- but his argument there digs deeper. Think about this: The eye cannot say to the hand, "I have no need of you," nor again the head to the feet, "I have no need of you." On the contrary, the parts of the body that seem to be weaker are indispensable, and on those parts of the body that we think less honorable we bestow the greater honor, and our unpresentable parts are treated with greater modesty, which our more presentable parts do not require. [1 Cor 12] What kind of plea is that, except to say that the church is not only made up of the strong, or of the great, but also of the weak, and in fact the weak are indispensible.
This is such a brilliant analogy -- especially when we consider what Paul has already said in 1 Cor 11: I hear that there are divisions among you. And I believe it in part, for there must be factions among you in order that those who are genuine among you may be recognized. You know: this is again an admonition that somehow the right ones must stay for the sake of the broken ones.
So in this, I ask you: is Paul really silent on whether or not we can or should leave a church? Or has he spoken to this problem already, requiring us not to abandon the church when it is weak and fallible, but to stay joined to it for Christ's sake, and the sake of those who are in error?
And I say all that to say two things to conclude the week:
 Keep this in mind as we go back to the GTY statement and consider what it says after its list of reasons a church may be corrupt.
 Be with the Lord's people on the Lord's day in the Lord's house this weekend because it is where you belong. This is where you are called out to, and while you need it, it most certainly needs you.