Symbolism, Imagery, Allegory
Today, when someone says "manufacture," we might picture a heavy-duty factory producing steel beams or something—but that would be large-scale industry, according to Marx. By manufacture, he means something earlier in history: the organization of handicraft laborers into a single workshop, where their proximity to one another and co-operation make production more efficient.
Basically, instead of a single person with an Etsy shop making clothes alone as a handicraft, imagine multiple people under the same roof making clothes in a more efficient way, each person only undertaking certain tasks. In manufacture, nobody makes the entire commodity from scratch.
So manufacture makes productivity go up, but the human rights cost is that workers become overspecialized. Workers might just turn a single screw over and over all day long instead of making the whole item and having a personal relationship with it. According to Marx, these workers suffer "the suppression of a whole world of productive drives and inclinations" (14.5.2) and become dumbed-down individuals: "Unfitted by nature to make anything independently, the manufacturing worker develops his productive activity only as an appendage of that workshop" (14.5.2).
Yup. The individual worker becomes just a cog in the manufacture machine.