What's "the most difficult thing about organ playing" ...?
Considering the fast pace of modern society, the needs of our usual vocations, what it takes to run a household, health issues, the need for refreshment and sleep, and the demands everything else makes on the new organist's time, the hardest thing about organ playing is just bringing one's self to sit on the organ bench and turn the instrument on !
"What's the most difficult thing about learning to play the organ?" is a separate question, one which personal bias can play a big part in answering depending upon who supplies the answer; for as many people as can be lined up, one will get just as many different answers depending upon how much difficulty they may have personally encountered with it in the beginning.
Someone might insist, hands down, that it's the touch.
Someone else might say that it's the fingering and hand division.
Others might swear that it's got to do with sight reading and transposition, or maybe improvisation.
A strong argument might be presented that the hardest thing about it is learning to get over the fear of the instrument, the fear of making a mistake, and the fear of playing it in public; but, then again, there are at least an equal number of players who aren't afraid of it at all and consider elements of pure technique more challenging, to them, than controlling their fears.
In a 4 part texture such as hymns, when moving to the organ from the piano, the hardest thing for the new organist to overcome seems to be getting the bass line out of the pinky of the left hand and sending it to the feet, then getting the left hand to work the tenor line all by itself.
Between our feet and left hand it's like we're all a little dyslexic in this respect, in the beginning; we read the bass line on the page but the instructions are carried out by the left hand instead of the feet; then we have to mentally associate parts with hands and feet to continue.
We can start out with having a fairly good background in piano playing and then along comes the organ with pedals, and now we're wanting to double the bass line with the left hand.
People who come to the organ without any piano background can notice the opposite problem; at some point, as they continue to grow as an organist and discover Bach and all the other rich literature for the instrument that has them captivated, and the desire to play it becomes almost overwhelming, they realize that they're going to need to come to terms with the piano to get where they want to go with the organ (it's like hitting a brick wall), and, when they move to the piano, associating the bass line with the pinky of their left hand is something new for them; it's the reverse situation, and some of them might encounter trouble with that, at first.
In both cases, it's the same neurological explanation:
The pedal part, as far as our brain is concerned, is like a 3rd hand that expects the brain to develop new neural pathways that are not there; it's like learning to ride a bicycle, at first we stumble, we fall, we trip, but eventually we get better with practice; after that we still tend to stumble, fall, and trip, but less with more practice.
The more neural pathways we have in our brain, the faster we're able to get the left hand and feet coordination going.
It's a problem that in the beginning just about all of us have more or less success trying to eradicate; very few can escape it.
And since the majority of people are right-handed, this might also have something to do with it.
Those left handed people who have taught organ seem to have the same issue with coordinating the left hand and pedal (the previous experience of performing hymns and other pieces on the piano seems to have more to do with this than being right of left handed.
Everyone is different ... the adjustment seems to be very easy for some, they might not even encounter the problem, but for others it might take a long time to make it work.
The important thing for the new organist to remember is: All of this is normal.
Objectively then, in terms of playing its music, the absolute hardest thing about learning to play this instrument -- the thing that would probably get the most votes -- is overcoming the challenge of getting the left hand and feet (photo) to coordinate, to move independently and exactly in time with the right hand ... a challenge made more challenging by continuing to indulge in the habit of doubling the bass with the left hand when playing 4 part hymns.
This habit leads can lead to difficulties later on when trying to learn contrapuntal repertoire, particularly fugues, which have independent parts for the left hand and feet [See blog, How To Learn A Fugue].
How well an organist has met that challenge can be tested by playing in a 3 part texture where there are never more than 3 notes sounding, simultaneously.
This can have the player on a bit of a slippery slope, trying to get all 3 moving lines to sound exactly in time, as any error in timing, no matter how slight, will be heard clearly.
Organists have coined the term "cow on ice" to describe the situation when they're trying to play a trio like this [See menu bar, Free Stuff, Trio in Eb Major Op. 14].
The important thing to remember here is not to get intimidated, to first practice each line separately, one at a time (right hand, left hand, pedal), then practice left hand and pedal, then both hands, before trying to put all 3 together [See blog, Getting Started With Writing, Part IX].
Here the left hand and pedal parts may have to be repeated more times until we can play it 3 times in a row without mistakes, as most people are right handed and their left hand is not quite as skilled or dexterous to start with.
Whenever difficulty is encountered playing trios like this it's almost always due to not taking the time to divide the practicing and take it at a slow tempo (about half concert tempo).
By practicing all the combinations an equal number of times, we're apt to notice the left hand and pedal together requiring more practice.
The left hand and pedal part often need to be practiced more than the right hand and pedal part even when we're left-handed, and so, it's just a good idea, when learning a new piece, to expect this will need a modicum of attention.
If the left hand part is tricky it should be practiced enough so that mistakes don't happen; typically, this is more than one time through without making a mistake.
Beginners tend to practice until they can get it right one time, then stop; actually, we need to keep practicing it until we can play it several times without mistake, then get it into memory that way.
Since the left hand is typically a little weaker also than the right hand, it will also help to practice the manual parts of organ pieces on a piano or an electronic stage piano which has the actual touch and feel of a real piano.
Practice on a mechanical action organ generally provides the necessary key resistance to form a foundation for finger strength, but some older historic instruments without Barker pneumatic assist action can be very difficult to play, even for virtuosos, and hard on the hands after a while; on the other hand, habitual practice on electronic keyboards and pipe organs with very light electropneumatic actions typically have keys which are too easy to depress and tend not to develop the left hand very well, to bring it up to speed with the right hand.
For an organist, it helps to practice Czerny (pronounced "chair'-knee") etudes on the piano to help develop the left hand and build equal strength in both hands.
Carl Czerny was a piano pupil of Clementi, Hummel, and Beethoven and a prolific composer who wrote tons of studies for the piano (over a thousand works), most of which have passed into oblivion today, but some of his works have survived and are still recommended by piano teachers [See blog, What About The Piano, Part IV].
It helps to work from a copy of Czerny's "The Art of Finger Dexterity Op. 740."
There will be an improvement in finger strength, especially in the left hand, by working just the first etude (in C Major) from this book (which isn't terribly hard to read, or to learn).