The third line turns the wagon's load toward a purpose beyond itself. Legge's translation describes a feudal lord offering what he holds in tribute to the emperor, an image of abundance actively directed upward and outward rather than kept for private use, and the text notes plainly that small, selfish men are not capable of such generosity. Where the second line proved capacity, the third line proves character: strength and possession are only as good as the use they are put to, and here that use is service rather than accumulation.
This is the topmost line of the lower trigram Qian, the last position before the hexagram crosses into the upper trigram Li, and Chinese commentary reads such threshold lines as moments where a hexagram's deeper virtue is tested most directly. Great Possession could easily become a hexagram about hoarding; this line insists otherwise, making the transition into the upper trigram contingent on abundance already proving itself generous rather than merely large.
Read against the hexagram's full sequence, the third line answers a question the first two lines leave open: what is great possession actually for. The feudal lord's tribute supplies the answer before the hexagram moves any further, and the explicit exclusion of small, selfish men marks generosity, not mere holding, as the quality Great Possession asks its abundance to serve.