[Because this two-volume work is a selection out of Vasari's biographical sketches, it doesn't make much sense to do an 'Opening Passage'.]
In the vicinity of Prato, which is at the distance of some ten miles from the city of Florence, and at a village called Savignano, was born Bartolommeo, according to the Tuscan practice called Baccio. From his childhood, Bartolommeo evinced not only a great inclination but an extraordinary aptitude for the study of design; and by the intervention of Benedetto da Maiano, he was placed under the discipline of Cosimo Roselli, being taken into the house of certain of his kinsfolk who dwelt near the gate of San Piero Gattolini, where Bartolommeo also dwelt many years, for which reason he was always called Baccio della Porta, nor was he known by any other name. (Vol 2, p. 5)
Summary: I found Vasari's work to be interesting for the same reason that I often enjoy biographies of poets: it is a look at art from the workmanship side, and takes the details of workmanship seriously. In a very real sense one can read Vasari's lives of the painters as a series of studies on the interrelation of talent, education, and reward in good painting, by one who was familiar with all three, and, interestingly enough, the relation of these three things in painting to good character in general, as part of that form of good life that is suitable to painters.
The first teacher of every painter is nature, and the painter by his designs seeks to imitate nature, selecting "the brightest parts from her best and loveliest features" (Vol. 1, p. 21). Some, like Giotto or Michelangelo, have an extraordinary innate talent and drive to learn from nature directly; they are, as Vasari says of Giotto, "induced by nature herself to the arts of design" (Vol. 1, p. 21). Those who are "by nature disposed to the cultivation of the arts" have a sure foundation for a good life, one which can be extended by study; this may be built upon by "character and manners calculated to render them acceptable to all men"; but to achieve true greatness one must be noticed (Vol. 1, p. 50).
The natural talent and study which makes good painting possible needs to be encouraged by reward, "for there are many minds, which might remain dormant if left without stimulus, but which, being excited by this allurement, put forth all their efforts, not only for the acquirement of their art, but to attain the utmost excellence therein" (Vol 1., p. 66). On the other side, however, we have the examples of painters like Sebastiano del Piombo that show that this is not a universal rule, however, good it may be in general:
...the liberality of just and magnanimous princes has, in certain instances, produced a contrary effect, seeing that there are many who are more disposed to contribute to the advantage and utility of the world while in depressed and moderate condition than when exalted to greatness and possessing an abundance of all things. (Vol 2., pp. 340-341)
We see something similar to this with study, which is essential to serious painting, but at the same time can be done badly. Thus the painter Paolo Uccello ruined his native talent by an excessive, almost obsessive, focus on studying perspective, and the quality of the work of Jacopo da Pontormo declined through his life because, instead of cultivating the excellences of his early style, he devoted himself to studied imitation of Northern European painters. As Vasari says in reflecting on the latter, "he who ventures to do himself violence and seeks to force nature does but ensure the ruin of those good qualities which had been imparted to him" (Vol. 2, p. 290). And Vasari repeatedly notes the importance of what one studies in one's youth -- a matter almost of accident, but which can have significant effects on the quality of one's work later. And study itself can get you only so far; as Vasari notes, providence, seeing so many artists struggling in "ardent studies pursued without any result" (Vol 2., p. 107), decided to show them the perfection of art by simply making Michelangelo.
A similar issue can be found with good character. You have painters like Fra Angelico, whose saintly character is part of his skill in painting, in a way that shows that the two are capable of combining in a powerful way. Vasari is likewise very clear that all of the greatest painters had at least some excellent character traits that made them admirable men as well as admirable painters, and that the two ways of being admirable are in some way connected -- and yet others may be overrated because their character gives them an ability to please that does not have much to do with the quality of their work.
We see then throughout the fragility of greatness of painting. Where natural talent is wanting, one can only get so far. But natural talent also requires cultivation, and each form of cultivation has pitfalls. The external cultivation of reward provides the incentives of wealth and glory to intensify the latent motivation to paint -- but in some cases it may have the opposite effect. The personal cultivation of study is a powerful thing -- but it may ruin or mislead as well as stimulate. And the innermost cultivation, that of good character, diligent, sweet-tempered, thoughtful, gives a grace to one's work -- sometimes. Painting itself is a fragile art -- Vasari is already full of stories of destroyed masterpieces -- but the conditions for great painting are themselves fragile. Talent, character, study, and reward: they all must come together, and do so in the right way, for real and lasting greatness to be achieved.
It is related that the prior of the monastery was excessively importunate in pressing Leonardo to complete the picture [of the Last Supper]. He could in no way comprehend wherefore the artist should sometimes remain half a day together absorbed in thought before his work, without making any progress that he could see; this seemed to him a strange waste of time, and he would fain have had him work away as he could make the men do who were digging in his garden, never laying the pencil out of his hand. Not content with seeking to hasten Leonardo, the prior even complained to the Duke, and tormented him to such a degree that the latter was at length compelled to send for Leonardo, whom he courteously entreated to let the work be finished, assuring him nevertheless that he did so because impelled by the importunities of the prior.
Leonardo, knowing the Prince to be intelligent and judicious, determined to explain himself fully on the subject with him, although he had never chosen to do so with the prior. He therefore discoursed with him at some length respecting art, and made it perfectly manifest to his comprehension that men of genius are sometimes producing most when they seem to be labouring least, their minds being occupied in the elucidation of their ideas, and in the completion of the conceptions to which they afterwards give form and expression with the hand.... (Vol 1, pp. 316-317)
Recommendation: It takes an interest in Italian Renaissance painters, but if you have that, it is definitely Recommended.