Shared ground
Joel 2:4–9 presents an advancing force as fast, loud, coordinated, and effectively unstoppable. The text piles up “like” comparisons (horses, chariots, fire) to make the audience picture and hear the approach, then shifts to the human effect: whole communities panic and faces go pale (v.6). It then stresses discipline: they keep formation, do not collide, and do not break ranks even when meeting resistance (vv.7–8). Finally, normal protections collapse—walls, city space, and private homes are all penetrated; they enter windows “like thieves” (v.9).
Where interpretation differs (only where needed)
The main question is what this “army” is. Some read it as a literal locust swarm described with military imagery: the “horse/chariot” language highlights how locusts look and sound, and the swarming over walls and into houses matches insect behavior. Others read it as human soldiers (or an invading army) described with imagery that makes them feel like an overwhelming plague: disciplined ranks, breaching defenses, and storming a city sound like military assault.
A related difference is how to take “like thieves” (v.9). Some hear emphasis on suddenness and surprise. Others hear emphasis on total vulnerability: even private, interior spaces are no refuge.
Why the disagreement exists
The passage intentionally uses comparison language rather than naming the force directly, and the broader context in Joel moves between ecological disaster imagery and invasion imagery (within the wider “day” warning of Joel 2:1–2:11). Because the wording fits both a locust plague and a military attack at key points, readers weigh different details more heavily.
What this passage clearly contributes
Explicitly, the text portrays a coming crisis that cannot be contained by normal defenses: speed, sound, fear, disciplined advance, and total penetration (vv.4–9). Theologically (as an inference from the larger warning scene), it supports the idea that the “day” described in Joel is experienced as overwhelming and comprehensive—public and private life alike are exposed—whether the instrument is ecological, military, or a blended portrayal of both.