This sentence is dense: the main clause to grasp first is deprivation (yuḥramūn) from the benefits and fruits of knowledge. The appositive clause (“namely acting on it and spreading it”) names what those fruits are. Without ʿamal and nashr, knowledge does not yield what Allah made it for.
The diagnosis is not laziness alone; it is misreading the path (aḫṭaʾū ṭarīqah) and neglecting its conditions (tarakū sharaʾiṭah). “Whoever misses the path strays” (ḍalla) — in study, that often means failing to reach one’s aim, not only creedal error. Even a small aim (e.g. learning Arabic) fails without correct method.
In discussion, name two fruits plainly: living what you learn, and not hoarding benefit — spreading sound knowledge is part of the fruit. Modern questions about publishing rights belong with qualified scholars in fiqh and adab; the author’s principle here is spiritual: the dīn is meant to take hold of hearts and lives, which requires both implementation and transmission.
The ḥadīth on seeking a path of knowledge pairs well here: none of the named gates of Paradise is called “knowledge,” because knowledge orders action; those gates belong to the deeds knowledge awakens.