And of Zebulun he said, “Rejoice, Zebulun, in your going out, and Issachar, in your tents. They shall call peoples to their mountain; there they offer right sacrifices; for they draw from the abundance of the seas and the hidden treasures of the sand.”
Deuteronomy 33:18-19 ESV

Tradition says Zebulun was made to be a merchant tribe so they could support the scholarly work of Issachar.