My eye has acted like a painter and engraved your beautiful image on the canvas of my heart. My body is the frame that holds this picture; to draw that picture with perspective, realistically representing depth, is the highest skill a painter could have. Only via this painter—my eye—can you find the image of you that dwells continually in my heart: Your own eyes are the windows into my heart.
Now look at the favors our eyes have done for each other: My eyes have drawn your shape, and your eyes are windows into which I can look to see my own heart, into which the sun also likes to look, taking a peep at your reflection.
Yet my eyes lack a certain skill that would grace the others they already have: They can only draw what they see; they don’t see into your heart.
Sonnet 24 is very difficult to follow even when translated. We are meant to picture the speaker and the addressee staring into each other’s eyes and each seeing his own reflection. The speaker is able to see through the eye of his own reflection into his own heart, where the image of the addressee is enshrined.