While this book is really well researched and speaks with the authority earned from being truly expert on the topic, most readers will find this pretty inaccessible because it assumes an audience who are already experts in Old English, Middle English, and early Modern English including their sundry dialects over its history. I am an English and linguistics major and an English teacher who has read a great deal on this topic and historical linguistics, yet I still found this book quite inaccessible in large sections.
The majority of the source texts come from the Christian bible or from the featured period's thinkers philosophising or teaching on religion, faith, and Christianity -- there is no other topic that induces me to boredom or tunes me out more than other people describing their magical thinking and Christian beliefs, but disingenuously presenting them as fact.
At first I thought that there were so many religious texts because those were the only sources, but as we progressed into Early Modern English, it continued leaving me to think the author had a preference for these texts or a belief that they were the most authoritative representation of the language for each time. Basically, it felt like getting tricked into reading the bible.
The last straw was when I came across an explanation of a word in which this author casually cites the word of early explorers to the "New World" (in other words, genocideurs, murderers, and slave traders) and slanders the First Nation group of the Carib people (Indigenous to Haspionola -- present day Haiti and the Dominican Republic) as being cannibals. He glibly calls this First Nations group cannibals, without citation, on the testimony of people who were ACTUAL slave holders, sadistic killers, and genocideurs.
Authors, the time where you get to say garbage like this and think you won't be explicitly called out for it is long over. It's notable as well that the crimes of Christopher Columbus and the rumours of cannibalism were both well known when this book was written, but the author chose to highlight the cannibalism, cite the genocideur as evidence, and then not mention the genocide, murders, rapes, beatings, or slave trading perpetrated by the white European genocideur.
Fortunately, I have read many texts in which the Carib people are actually given a voice and allowed to talk and I know that this claim of cannibalism is WIDELY DISPROVEN.
The authority of this entire book is undermined by the casual repetition of the slurs of genocidal early explorers as fact.
For a far better, more accessible, and less cringey treatment of the same topic, try Elly Van Gelderen's "A History of the English Language".