The main conflict of story centers around the beliefs of most flatlanders: since - as far as they are concerned - 3 dimensional objects are impossible and don't exist, anyone who claims they are possible (or has seen one)  is either insane or dangerous or both, and thus must be placed permanently in a mental institution or must be put to death.

Without delving any further into the story, let me point out what Abbott so masterfully illustrates using concepts that we, as 3 dimensional beings, readily understand by his analogy:

1. Just because a truth is difficult to understand in our physical realm, doesn't make it either impossible or irrational.
   In the search for the "Theory of Everything" (TOE) Many scientists today believe in the scientific theory known as "String Theory" or its variant "M" Theory which requires 11 dimensions. (If you include time we know of 4 of the needed dimensions;  they have no problem with the fact that we have difficulty in finding the other 7; but interestingly, an unseen spiritual dimension (or dimensions) filled with unseen spiritual beings is a  problem for many.)
    
2. Just because a truth is not popular doesn't make it untrue or irrational.
   (That's the logical fallacy known as "argument from popularity" or "appeal to the people")
    
3. Just because you don't believe or understand a truth doesn't make it irrational
   The Pythagorean theorem, typically expressed as a² + b² = c² states that the sum of the squares of the two sides of a right triangle is equal to the square of the hypotenuse. You may not believe it; you may not understand it; but neither of those conditions makes the statement untrue or irrational.
    
4. The majority typically don't like feeling incorrect or uninformed, and many don't like feeling unspiritual; nor will they long suffer the preaching of anyone trying to enlighten them.
   So what's the response? As Abbott shows, the typical responses are attempts to silence those who disagree with the majority. In the story we see the extreme cases (isolation from society; death); In our world we have the entire spectrum of attempts to silence unpopular truth. An obvious one being the unpopular truth that marriage was designed for one man and one woman - we're now seeing activists trying to 1) silence anyone who disagrees with the lgbt agenda and 2) trying to force everyone to agree with them or suffer the consequences.

In short, applying subjective criteria to a truth you don't like to show why it shouldn't be true doesn't make it untrue. (This is a typical argument for atheists who haven't realized the irrationality of the argument - I don't like X  therefore I don't believe in God.  [where X is what the atheist objects to: evil in the world, having to be moral, not being master of their own destiny, etc.]) That is a totally irrational approach, yet if you Google "why I don't believe in God" you'll find it's a common approach.  It's like saying I don't like the Pythagorean theorem, therefore it's not true. Likewise, applying subjective criteria to an untruth to make it palatable doesn't make it true.

I say this in preparation to further define what Rational Faith is.  In my previous post I discussed what Rational Faith is not. In a sentence - rational faith is not in conflict with either reason or science; nor does it pit science against faith because properly understood, science and Christian faith properly practiced both lead to truth in the areas to which they address themselves.  And now let me state upfront - keeping in mind the statements above:

The Christian faith is true, therefore it is rational. 
  It's true:

• Whether or not you believe it to be possible or not
• Whether you believe it to be popular or not
• Whether you understand it or not
• Regardless of whether it makes you feel uncomfortable or not

Someone will no doubt ask what makes believing "the Christian faith is true" a rational proposition? The fact that it's true. They'd ask how do I know it to be true? And I'd respond how does the rational person know anything is true? By evidence. And there are many lines of evidence the Christian can produce - starting first and foremost with the resurrection of Jesus Christ. Having evidence to support what is believed makes it rational, as opposed to relying solely on the authoritative word of scripture - which some understand as "taking it by faith". ( Incidentally, you can trust the Bible since it is true and authoritative, but logically speaking for those who want confirmatory evidence, relying solely on scripture invokes the circular argument fallacy.)

Two approaches Demonstrating that Christianity is a Rational Faith

Approach 1: A proper understanding of faith

A better question than "is it rational"  is this:  "is what Christians have really faith?" Because from the perspective of  the unbeliever, what Christians espouse is unadulterated faith since the Christian can not prove what they believe to their satisfaction.  Notice this does not make what the Christian believes untrue. But On the part of the Christian - what may start as faith  winds up as certain knowledge because the Christian has a totally different understanding of  faith - which comes from scripture:

Now faith is being sure of what we hope for and certain of what we do not see.
Hebrews 11.1

Thus the Christian - at least those who are mature in their walk with Christ - will tell you what she or he has is not faith as most understand it, but rather certain knowledge based on evidence as well as life experiences. This is the natural (and intended) consequence of  living an authentic Christian life. For further clarification, let me elucidate the following statement based on the text above.

There is no uncertainty involved in Christian faith
Please note that:

• The Christian faith is a not a vague hope
  - Not based on distant pie in the sky by and by promises. It's specific and concrete.
   
• It's not a faith without any basis in fact or history;
  The life, death and resurrection of Jesus Christ is well documented.
  It is an evidence based faith.
   
• It's not something you must believe in spite of  certain tenets being contradictory to reason.
  Just because something is not part of common experience doesn't make it contradictory to reason.
  Just as experiencing a sphere was not a common experience for a flatlander; that does not make the concept of a "sphere" contradictory to reason.
  Likewise experiencing God may not be a common experience. That does not make the concept of God irrational or untrue. In fact the respected philosopher Alvin Plantiga in his Ontological Argument for the existence of God demonstrates that if you merely accept the possibility that God might exist then God must necessarily exist. (Take note all you agnostics.) Of equal importance for our discussion is what he concludes:
  
  "What I claim for this argument, therefore, is that it establishes, not the truth of theism, but its rational acceptability"¹ (emphasis mine)
  Alvin Plantiga
   

The point - a mere assent to the concept that God could exist establishes the concept of God as a rational proposition, which would make believing in such a God a rational proposition.

Approach 2: A proper understanding of Rational

That Christianity is a rational faith can also be demonstrated by looking at  the meaning of  "rational".  According to Webster's dictionary Rational is:

"having reason or understanding; relating to, based on, or agreeable to reason;"² "based on and in accordance with reason or reasoning"³

It other words, rational means all the things you'd expect it to mean:

• There are reasons involved; it is not merely claims with no evidences backing them
• It doesn't break the laws of reason or logic
• It is internally consistent

Notice what is not included - being reasonable does not mean being in agreement with all the current theories of science. Because these days, science by definition excludes anything that is beyond the natural world - regardless of whether or not such things might exist. John Rennie, editor-in-chief of Scientific American, in defining the scientific tenet of methodological naturalism puts it this way:

Such an approach may be helpful for scientific experimentation; but it is not helpful  for rational deliberation.

As I look at that definition it's clear that this definition would likely find a home in Christian enclaves but would raise hackles in non-Christian circles. The objectionable part is the first sentence - "certainty" which could be argued to be coming from a reliance on scripture (instead of evidence), so let's just remove references to certainty and with it, any possible reliance on scripture. That leaves us with:

Rational Faith is:

Confidence in the rational nature of the Christian faith based on numerous lines of evidence, and strengthened by reasonable arguments and concepts which do not break the laws of logic, and which are (along with its resulting worldview)  internally consistent.

This concords well with how theologian RC Sproul speaks of rational faith:

"But what he [God] reveals is intelligible; we can understand it with our intellect. He doesn’t ask us to throw away our minds in order to become Christians."⁶

And perhaps most importantly, this demonstrates that contrary to popular opinion, faith - by which I mean rational faith - does not require a leap of faith. Because rational faith is built step by step, on evidence upon evidence - not irrational, inconsistent beliefs. Now if Christianity is rational and internally consistent, that might lead one to conclude that Atheism is irrational and not internally consistent. That is true and worthy of further discussion, but that is a topic for yet another post.