The first aliyah begins with the description of the duties of the family of Gershon. First G-d instructs Moshe to count the members of the Gershon family between 30 and 50 years old. Then G-d gives their service, which is to carry all the tapestries, and the veil and coverings of the Mishkan whenever the Jewish people journeyed.
Then a similar counting is done of the Merori family and their duties are described: they carry the structural members of the Mishkan, such as the beams, boards, pillars, etc.
