What does 1 Samuel 8:18 mean?

Samuel comes to the end of this extended "fair warning" about what the Israelites should expect from an earthly, human king. They had never had a human king before. Instead, the Lord had been Israel's Ruler, blessing them when they were faithful to Him and turning them over to their enemies when they served foreign gods.

The Lord wanted Samuel to give this legal-sounding disclaimer to the people before they decided finally that they wanted a human king to rule over them. Since human kings have absolute authority and power in their kingdoms, Samuel warned the Israelites about how power can be abused. In fact, the more power given to a human leader, the more likely they are to abuse it. Israel is cautioned that kings will take their children as servants and their property and a percentage of their harvest and flocks. In general, they are gaining a "chain of command" but sacrificing their freedom in almost every other way. They would exist to serve the king to whatever degree the king demanded it.

Finally, Samuel warns that when these things happen, the Lord will not answer the cries of the people for help. They will have chosen this for themselves (1 Samuel 8:4–5). Since the people want to be like the other nations in having powerful kings, they will suffer like the citizens of other nations under the heavy hand of human rulers.