Both pieces refer to the Christian theme of the Annunciation and provide support to the main elements of the altarpiece. Most of Van Eyck's work was along similar lines, other than the occassional portrait. Very little of his work actually survived to the present day, unfortunately, with only 3 or 4 study drawings confidently attributed to this Netherlandish master.
The artworks feature ribbons with Latin writing which confirms their respective figures and each one also wears particularly draping clothng which just about fits into these particularly small panels. Whilst beautiful, these two figures were never intended to take too much attention and serve on the outside of the overall piece.
With so little work remaining from this artist's career, each and every individual panel has been researched and studied in great detail in order to maximise our knowledge of this exceptional artist. The overall project was so significant that it is likely that he produced many study drawings for each panel, but these are not available today.