What we read with inclination makes a much stronger impression

I came across a quotation from James Boswell's Life of Johnson alluding to the importance of purposefulness in reading if it is to have some measurable effect on life outcomes. Johnson's term is "inclination", i.e. interest. I went to Life of Johnson to verify and came across a series of worthwhile observations by Johnson about reading, writing, and learning. I do not share all of his views, but interesting none-the-less.

In the edition I referenced, there is an Introduction by Charles Grosvenor Osgood.

The Life of Johnson is not a book on first acquaintance to be read through from the first page to the end. 'No, Sir, do YOU read books through?' asked Johnson. His way is probably the best one of undertaking this book. Open at random, read here and there, forward and back, wholly according to inclination; follow the practice of Johnson and all good readers, of 'tearing the heart' out of it. In this way you most readily come within the reach of its charm and power. Then, not content with a part, seek the unabridged whole, and grow into the infinite possibilities of it.

But the supreme end of education, we are told, is expert discernment in all things—the power to tell the good from the bad, the genuine from the counterfeit, and to prefer the good and the genuine to the bad and the counterfeit. This is the supreme end of the talk of Socrates, and it is the supreme end of the talk of Johnson. 'My dear friend,' said he, 'clear your mind of cant; . . . don't THINK foolishly.' The effect of long companionship with Boswell's Johnson is just this. As Sir Joshua said, 'it brushes away the rubbish'; it clears the mind of cant; it instills the habit of singling out the essential thing; it imparts discernment. Thus, through his friendship with Boswell, Johnson will realize his wish, still to be teaching as the years increase.

Observations by Johnson himself.

A man ought to read just as inclination leads him; for what he reads as a task will do him little good. A young man should read five hours in a day, and so may acquire a great deal of knowledge.

[snip]

He had no settled plan of life, nor looked forward at all, but merely lived from day to day. Yet he read a great deal in a desultory manner, without any scheme of study, as chance threw books in his way, and inclination directed him through them. He used to mention one curious instance of his casual reading, when but a boy. Having imagined that his brother had hid some apples behind a large folio upon an upper shelf in his father's shop, he climbed up to search for them. There were no apples; but the large folio proved to be Petrarch, whom he had seen mentioned in some preface, as one of the restorers of learning. His curiosity having been thus excited, he sat down with avidity, and read a great part of the book. What he read during these two years he told me, was not works of mere amusement, 'not voyages and travels, but all literature, Sir, all ancient writers, all manly: though but little Greek, only some of Anacreon and Hesiod; but in this irregular manner (added he) I had looked into a great many books, which were not commonly known at the Universities, where they seldom read any books but what are put into their hands by their tutors; so that when I came to Oxford, Dr. Adams, now master of Pembroke College, told me I was the best qualified for the University that he had ever known come there.'

[snip]

Talking of education, 'People have now a-days, (said he,) got a strange opinion that every thing should be taught by lectures. Now, I cannot see that lectures can do so much good as reading the books from which the lectures are taken. I know nothing that can be best taught by lectures, except where experiments are to be shewn. You may teach chymistry by lectures.—You might teach making of shoes by lectures!'

[snip]

He then took occasion to enlarge on the advantages of reading, and combated the idle superficial notion, that knowledge enough may be acquired in conversation. 'The foundation (said he,) must be laid by reading. General principles must be had from books, which, however, must be brought to the test of real life. In conversation you never get a system. What is said upon a subject is to be gathered from a hundred people. The parts of a truth, which a man gets thus, are at such a distance from each other that he never attains to a full view.'

[snip]

He said, that for general improvement, a man should read whatever his immediate inclination prompts him to; though, to be sure, if a man has a science to learn, he must regularly and resolutely advance. He added, 'what we read with inclination makes a much stronger impression. If we read without inclination, half the mind is employed in fixing the attention; so there is but one half to be employed on what we read.'

[snip]

Dr. Johnson advised me to-day, to have as many books about me as I could; that I might read upon any subject upon which I had a desire for instruction at the time. 'What you read THEN (said he,) you will remember; but if you have not a book immediately ready, and the subject moulds in your mind, it is a chance if you again have a desire to study it.' He added, 'If a man never has an eager desire for instruction, he should prescribe a task for himself. But it is better when a man reads from immediate inclination.'

[snip]

Snatches of reading (said he,) will not make a Bentley or a Clarke. They are, however, in a certain degree advantageous. I would put a child into a library (where no unfit books are) and let him read at his choice. A child should not be discouraged from reading any thing that he takes a liking to, from a notion that it is above his reach. If that be the ease, the child will soon find it out and desist; if not, he of course gains the instruction; which is so much the more likely to come, from the inclination with which he takes up the study.'

[snip]

On Thursday, May 1, I visited him in the evening along with young Mr. Burke. He said, 'It is strange that there should be so little reading in the world, and so much writing. People in general do not willingly read, if they can have any thing else to amuse them. There must be an external impulse; emulation, or vanity, or avarice. The progress which the understanding makes through a book, has more pain than pleasure in it. Language is scanty, and inadequate to express the nice gradations and mixtures of our feelings. No man reads a book of science from pure inclination. The books that we do read with pleasure are light compositions, which contain a quick succession of events. However, I have this year read all Virgil through. I read a book of the Aeneid every night, so it was done in twelve nights, and I had great delight in it. The Georgicks did not give me so much pleasure, except the fourth book. The Eclogues I have almost all by heart. I do not think the story of the Aeneid interesting. I like the story of the Odyssey much better; and this not on account of the wonderful things which it contains; for there are wonderful things enough in the Aeneid;—the ships of the Trojans turned to sea-nymphs,—the tree at Polydorus's tomb dropping blood. The story of the Odyssey is interesting, as a great part of it is domestick. It has been said, there is pleasure in writing, particularly in writing verses. I allow you may have pleasure from writing, after it is over, if you have written well; but you don't go willingly to it again. I know when I have been writing verses, I have run my finger down the margin, to see how many I had made, and how few I had to make.'