Deuteronomy 17:14
When thou art come unto the land which the LORD thy God giveth thee, and shalt possess it, and shalt dwell therein, and shalt say, I will set a king over me, like as all the nations that are about me; When thou art come unto the land which the LORD thy God giveth thee, and shalt possess it, and shalt dwell therein, and shalt say, I will set a king over me, like as all the nations that are about me;
Moses foresaw that after Israel entered the land the Lord would give them, took possession of it, and settled in it to dwell there, they would desire and receive a king like the surrounding nations. That foresight did not mean kingship was God's preferred form of government for Israel, nor that a king would be best for His people. Their demand for a human monarch rejected His special leadership through the rulers He chose and the prophets through whom He governed them, showing a lack of faith in His providence.
A king would bring spiritual dangers, since the people might give an earthly ruler the honor due to God, and a king whose heart was not right with God could lead them into rebellion. The authority and honors of kingship could exalt a ruler so that his own ways seemed right to him while he sinned against God, and by a king's command innocent people could suffer and unworthy people be raised up unless he continually trusted God for wisdom. God may permit people to follow their own course when they reject wise counsel, and in this case He granted the people's request through Samuel while solemnly warning them of His disapproval and of the consequences of having a king.
Providing for a king did not consent to a change in the principles on which the state was founded, for the government was still to be administered in the name and by the authority of God. God was still to be recognized as the head of the nation and His law enforced as the supreme law of the land, with the king serving only as vicegerent of the Most High to enforce the laws God had given and with no authority to legislate for the nation. The king was to be chosen by the Lord, a right God reserved to Himself, and Israel honored this by leaving the selection entirely to Him when the choice fell upon Saul.