דברי הימים א, פרק כ״ד, פסוק ו׳

The organization of the priesthood required a structured system to ensure fair and orderly service. Dividing the priestly families into specific shifts was accomplished through a highly public and official lottery, conducted in the presence of the highest political and spiritual leadership. Shemaiah the scribe was appointed to document the families, an act that served two vital purposes. First, it involved preparing the actual slips of paper bearing the names of the ancestral houses, which were then placed into a ballot box for the drawing [מצודת דוד]. Second, the documentation created a permanent historical record, establishing an enduring memory of the exact order of the shifts to dictate who would serve first, second, and so on [רש״י].

As the lottery was organized, a clear numerical distinction emerged between the descendants of Eleazar and those of Ithamar. Originally, both lineages had an equal standing of eight ancestral houses each. However, King David observed that the family of Eleazar had grown significantly larger over time. To accommodate this growth, he divided each of Eleazar's ancestral houses in two. Consequently, every ancestral house of Eleazar effectively absorbed an additional family group, while the family of Ithamar remained in its original, unchanged configuration [מצודת דוד]. In practical terms, this meant that the lineage of Ithamar was allocated exactly half the number of ancestral houses compared to the lineage of Eleazar [ביאור שטיינזלץ].

An alternative perspective explains the practical mechanics of how the lottery was drawn to reflect this imbalance. The leaders drew one slip from the family of Eleazar and then one from the family of Ithamar, alternating between the two lines. This alternating pattern continued until the seventeenth shift. Because of the numerical disparity, from the seventeenth shift onward, all remaining shifts belonged exclusively to Eleazar. In this view, the selection process highlights a distinct historical contrast. The shifts of Eleazar included newly added divisions, whereas the shifts of Ithamar were the original, ancient groupings established from the very beginning of the priesthood [מלבי״ם].