Zebulun is Leah's sixth and last son: "G-d has endowed me with a good gift; this time my husband will dwell with me, for I have borne him six sons" (Genesis 30:20). Two words answer each other in the sentence: zeved, the gift, and zevul, the dwelling.
Jacob gives him a place rather than a portrait: "Zebulun shall dwell at the shore of the seas; he shall be a haven for ships, and his flank shall reach toward Sidon" (Genesis 49:13). Note that Jacob names him before Issachar, his elder.
Moses takes up the pair again: "Rejoice, Zebulun, in your going out, and you, Issachar, in your tents. They shall call peoples to the mountain, there they shall offer sacrifices of righteousness, for they shall draw the abundance of the seas and the treasures hidden in the sand" (Deuteronomy 33:18 and 19). Zebulun goes out, Issachar stays: the two blessings are spoken together.
On the breastplate, according to the Targum attributed to Jonathan, his stone opens the fourth row: the tarshish (Exodus 28:20), often rendered as chrysolite or beryl; the identification remains uncertain. In the desert Zebulun encamps to the east, third after Judah and Issachar (Numbers 2:7), with Eliab son of Helon as prince. The Midrash cited by Ramban explains his place next to Issachar: he is the one who has wealth, and it cites the two verses, "at the shore of the seas" and "the abundance of the seas." According to Rashi, his banner had the color of his stone.
According to the order of the banners, Zebulun receives Sivan, the month of the letter Zayin (Sefer Yetzirah 5:2); in the Vilna Gaon's version, Zayin rules over walking. The Bnei Yissaschar writes it: "Zebulun for Sivan." The Shem MiShmuel, following the order of the Ari, links Sivan to Zebulun through Leah's word, "my husband will dwell with me." One may compare the walking of Sefer Yetzirah with the "going out" that Moses blesses; this is a reading, not a text. According to the order of birth, Sivan would go to Levi.
Keep this: Zebulun is blessed in movement, Issachar in the tent, and Moses names them in a single sentence. One goes out, the other studies, and each needs the other.