John Wesley on Deuteronomy 33:19

They - Zebulun of whom Moses takes more special notice. And so having dispatched Issachar in two words, he returns to Zebulun. The people - the Gentiles, either those of Galilee, which was called Galilee of the Gentiles, who were their neighbours; or people of other nations, with whom they had commerce, which they endeavoured to improve in persuading them to worship the true God. The mountain - That is, to the temple, which Moses knew was to be seated upon a mountain. Sacrifices of righteousness - Such as God requires. Their trafficking abroad with Heathen nations shall not make them forget their duty at home, nor shall their distance from the place of sacrifice hinder them from coming to it to discharge that duty. Of the abundance of the sea - They shall grow rich by the traffick of the sea, and shall consecrate themselves and their riches to God. Hid in the sand - Such precious things as either Are contained in the sand of the sea and rivers, in which sometimes there is mixed a considerable quantity of gold and silver. Or, Such as grow in the sea, or are fetched from the sandy bottom of it, as pearls, coral, ambergrease. Or, Such as being cast into the sea by shipwreck are cast upon the shore by the workings of the sea. It were well, if the enlargement of our trade with foreign countries, were made to contribute to the spreading of the gospel.