The first group comprises those who encountered the Messenger of Allah ﷺ and kept his company. The latter—those who have not yet joined them—are everyone who comes after them while remaining upon their path until the Day of Resurrection; their delay and failure to join, therefore, relate only to time.
Another interpretation of the verse is that the words “have not yet joined them” (1) refer to merit and rank (2): they fall short of the Companions in excellence, so their non-joining is a matter of status.
In truth, the two explanations are inseparable, for those who come after the Companions will never reach them—neither in virtue nor in time. These two categories, then, are the blessed ones.
As for anyone who refuses the guidance Allah sent with His Messenger and does not so much as lift his head toward it, he belongs to the third category: “those who were entrusted with the Torah but then failed to carry it” (3).
The Prophet ﷺ outlined the divisions of creation in relation to his call and the guidance (4) Allah entrusted to him when he said: “The likeness of the guidance and knowledge with which Allah has sent me is that of abundant rain that falls upon the earth. Part of the land is good and fertile; it absorbs the water and brings forth plentiful pasture and grass. Another portion (5) is hard and barren yet retains the water, so people drink from it and irrigate and sow their crops. A third portion is level ground that holds no water and produces no pasture. Such is the example of one who gains understanding of Allah’s religion—”