Quoting the commentary's own introduction:

In 2022, I began a preaching series on 1 John - a particular epistle we hadn't as a church previously paid explicit (systematic) attention to in my living memory. I became captivated by the way John carefully avoided giving a single command or instruction in the opening chapters. He appeared so concerned to lay out the facts first-and-foremost - it read to me like a legal case, and I was on the jury.

Piece by piece, he guided me through his line of thinking - building these arguments logically and gradually, so as to never leave anyone behind. Eventually, and climatically, he turns at the end of the epistle and as it were points at me, our eyes locked on one another. Then John simply and concisely tells me why this all matters so much. My assurance of salvation is at stake.

I've been fortunate. I've only ever very briefly tasted on the surface of my lips what it is to experience depression. It's struck unexpectedly a few times - and I fear it may be, as it is for one of my parents, something I will grow to know well.
That beloved parent of mine has suffered from bouts of terrible depression for many years - God, in His wisdom, has chosen to hand them over to hear all the lies one's mind conjures when every connection with reality is so severely compromised.

That's hard to watch as their son. And to see their spouse of 40 years fight to help them hold their grip on what's real and objectively true. God has taught me a lesson through all this: make the most of when He graces you the easy days. Saturate yourself with the teachings of such epistles as these - that if, in His loving wisdom, God chooses to hand you also over to these dark places for a time and a season - you may recall as Christ did - "It is written".

During my final drafting of this book, the four of us (me, my parents, and my wife) attended Ligonier's 2023 UK conference. During a Q&A session, Dr Sinclair Ferguson answered a question regarding assurance of salvation for the Christian. His answer, as always, was neither rushed nor impersonal, but rather pastoral and careful. With a clear concern and deep love for whoever was asking the question - he simply said he would advise them to find someone trustworthy to take them through 1 John.

My hope and my prayer is that this little book - as faulty as it is, as short as it stands, may help you navigate these three epistles more easily - and successfully draw your attention to at least most of the key points therein. If you have opened this book in desperate hope of finding immediate answers to concerns about your salvation, I implore you to seek wise and faithful counsel - and pray. Pray like there's no tomorrow. And consider skipping ahead to page 92 in this book where 1 John 5:13 is examined in a little detail.

Don't let this book alone sit on your bookshelf as "sufficient for understanding John's epistles". Find yourself other resources - better than this - to further saturate yourself.

I look forward greatly, by God's grace, to seeing you in the new heavens and on the new earth - to hear your testimony of God's grace in your own life, as I share His in mine.