The truth is that reading is inherently difficult, and English is particularly so because of its multitude of irregular spellings: for example, the different pronunciations of "ough" - "Though the rough, tough, cough and hiccough plough me through, o'er life's dark lough my course I still pursue". Part of the explanation lies in the mixed Celtic, Viking, Germanic and French origins of the English language, all of which jostle for recognition in the script. But probably the most important influence complicating spelling was status - an unholy alliance of the upwardly-mobile middle-class with the teachers they supported. A long time after the invention of printing, even Shakespeare spelt his own name in many different ways. But soon good spelling began to define how well educated you were. So to keep the in-crowd privileged, spelling had to be kept fiendishly difficult.
Unfortunately, the human brain is not well adapted for reading. It is the most complex skill that most of us who don't aspire to be concert pianists or advanced mathematicians have to master. To modern schoolchildren, it is not much different than for the 13th-century Florentine monk who wrote: "Reading is a painful task. It extinguishes the light from the eyes. It bends the back. It crushes the viscera and the ribs. It brings forth pain to the kidneys and weariness to the whole body."
Before writing was invented, we never had to be able to pick up tiny visual details in letters - a tree is a tree whether upright, upside down or back to front, and one important thing we learn is to identify it from all these different perspectives. But these transformations do matter with letters. A "d" changes to a "p", "b" or "q". Likewise, "dog" becomes "god" or "was" becomes "saw" if you get the order of letters wrong. In fact, learning to focus attention on sequencing these tiny details for reading carries costs to our ability to see overall shape, form, symmetry and balance. Often children and dyslexic poor readers are better at seeing large-scale relations across whole scenes and information fields than good readers. That may be why dyslexics so often make good artists and entrepreneurs.
Although reading is primarily a visual process, we also need to learn to split spoken words down to separate sounds, or phonemes, which in English are represented by letters. So you also have to learn to attend to the sequence of the sounds in a word. Children only learn that you can split the whole sound "dog" into separate sounds "d" "o" "g" after they've learnt that you can represent the word visually by the three letters "d", "o", "g". These phonemes are characterised by changes in their frequency and amplitude, so our auditory system has to pick up these transients very sensitively. This is analogous to sequencing the letters and letter features that we have to do visually when reading.