The book itself is in Descriptive Notation and I think Z-B assumes too much understanding on the part of his readers. Like many other authors he writes things like, "And White is clearly better and wins". The best way around this is to examine the example with an engine. The thing is though, many times this method reveals incorrect analysis or missed tactical chances. But that’s not unusual in books written in the pre-computer days.
Here are Znosko-Borovsky’s comments on Threats from his analysis of a Tarrasch-Janowski game fragment:
“Nearly all maneuvers which we undertake to achieve out aims are in the nature of threats and these threats at times may in themselves represent an object for which we strive. A threat is…the surest means of maintaining, if not increasing, any advantage we may have…there are direct threats by which the enemy is attacked once and then the distant or deferred threats, the effect of which become manifest only after a series of moves…the immediate threat harasses the enemy and may deprive him of all freedom of action; the second…is less obvious and therefore more difficult to fathom. It requires time to evolve an adequate defense and it may be said that in general it is the more decisive and in any case the more dangerous of the two.”
In the following example Z-B examines the position after 26…Qe7 and observes:
“In this example we see a whole series of threats which arise in turn without any respite. Black manages to defend himself against each single threat, direct and immediate, but succumbs in the end to the most distant one. This is a perfect illustration of the best possible exploitation of the distant threat; an uninterrupted chain of direct threats which allows the adversary no leisure to provide against the danger which lurks in the background. The time will come when two threats will occur: a direct threat and the distant threat which has now become immediate. It’s possible to parry one of the two but not both.”