whether they are female ("ladies") or male ("knights").
As he reads this literature that contains descriptions of beauty, the speaker is reminded (in the second quatrain) of the beauty of the young man. In fact, to him it even seems like the writers and poets of long ago were actually writing about the young man.
The point that these descriptions prefigure the beauty of the young man is clearly stated in the third quatrain. The speaker feels that these older writers were poet-prophets. In writing about the beauty of this lady or that man, they were actually writing about the beauty of the young man, whom they saw as if in a vision. These poets looked, the speaker states, with "divining eyes" (line 11). That is, they were able to see into the future. However, because they could only see the young man in a vision, but not in person, they could not capture fully the greatness of the young man's beauty in their poetry:
(line 12)
The speaker, then, is actually saying in this sonnet that all of the best descriptions of beauty ever written in literature are indications of the young man's beauty. However, such descriptions are incomplete or inadequate. The beauty of the young man far surpasses even the best of those descriptions.