This is a two part series by Pink. The second book (this one) is unfinished in the eyes of Pink.

From the book's foreword:
When we completed our 1,500-page exposition of John’s Gospel more than twenty years ago, we were urged to take up
the First Epistle of John, but felt quite incompetent to engage in it. The closing books of the New Testament, as their position indicates, require their expositor to possess a fuller knowledge of God’s Word and a more mature spiritual experience than do the earlier ones. The style of John’s Epistle is quite different from that of the other apostles, being more abstract, and for that reason more difficult of apprehension and elucidation. We still feel very unfit for the task upon which we are now entering, but if we wait until we deem ourselves spiritually qualified it will never be essayed. During the past quarter of a century we have given no little prayerful thought to its contents, and have studied carefully all the writings of others on it which the divine providence has brought our way. The benefits of, and gleanings from this we shall now share with our Christian friends.

Not only is John’s Epistle much more difficult than his Gospel (which is manifestly designed for babes in Christ, though even the ‘fathers’ never outgrow it) and the other apostolic writings, but it does not lend itself so readily to expositions of equal length. Some of its contents afford much more scope to a sermonizer than do others; and thus, while a whole article may be profitably devoted to certain single verses, others require to be grouped together, and because of this the reader is likely to be disappointed at the varying lengths of their treatment. It is perhaps for these reasons that comparatively little has been written upon this epistle—scarcely anything during the past fifty years. So far as we know, none of the Puritans attempted a systematic exposition of the same, for N. Hardy’s (1665) scarcely comes under that category. Yet this portion of God’s Word is equally necessary, important, and valuable for His children as are all the others, though what they are likely
to get out of it will largely depend upon their acquaintance with all preceding books and with the constancy and intimacy of their communion with the Triune God.