Exodus 34:16
And thou take of their daughters unto thy sons, and their daughters go a whoring after their gods, and make thy sons go a whoring after their gods. And thou take of their daughters unto thy sons, and their daughters go a whoring after their gods, and make thy sons go a whoring after their gods.
The prohibition stands where divine mercy, long-suffering, goodness, truth, and forgiveness are proclaimed together with the declaration that the guilty will not be cleared, where worship and intercession are offered for pardon and for the people to be taken as a divine inheritance, and where favor is renewed with promise of marvelous works on their behalf. It belongs to the renewed covenant made when forty days and nights were spent alone on the mount under miraculous sustenance, with no man allowed to ascend with him and none allowed to approach the mount during that absence, after two tables of stone had been prepared by command and the words of the covenant, the ten commandments, were written upon them by the Lord.
Taking the daughters of the inhabitants of the land as wives for sons is forbidden because those daughters pursue their gods in spiritual unfaithfulness and draw sons into the same unfaithfulness, so that intermarriage with idolaters and with Canaanites who worship other gods turns Israel and the people of God away from God toward idolatry. The command against such intermarriage is a safeguard against idolatry, against loss of loyalty to God, and against being led away from Him. It calls for serving the Lord God of Israel with all heart, soul, and mind rather than uniting with others and accepting places and practices that do not glorify God.
Neither political nor commercial advantage, nor the hope that the unbelieving spouse will be converted, justifies setting the command aside. Solomon’s marriages to heathen princesses illustrate the result of setting it aside, leading to the adoption of idolatrous customs and to national apostasy. The same warning was applied when a wife was sought for Isaac not from the Canaanites but from kindred who believed in the true God. In that application the servant was charged not to choose a Canaanite wife for Isaac, to seek a wife among kindred who believed in the true God, and not to take Isaac back to their country.
The requirement shows part of what God demands of His people and leaves no excuse for carelessness and indifference about which day to keep, since God has specified the seventh day in His Word and not the first day of the week.