What does 1 Samuel 8:15 mean?

At the Lord's direction, Samuel is being as blunt as possible to warn Israel about having a human king (1 Samuel 8:4–5, 9). The problem with kings is that they have nearly absolute power over the citizens they rule. Absolute power nearly always leads to corruption. Centralizing power in human hands may be more "efficient," but it is also ripe for abuse.

In addition to taking some of his citizen's children to be his own servants and taking some of their fields and vineyards to give to his own high-ranking officials (1 Samuel 8:10–14), the king will tax the harvest of his people. Samuel says that he will take a tenth or a "tithe" of the grain and the grapes to give as payment to his servants and officials.

On one hand, this makes some sense to modern readers. We're familiar with government taxing income to function properly—and there are legitimate purposes to human government (Romans 13:1–7). The tax described here seems to be different: the money is going to feed the king's own officials and servants. The tax might not necessarily be meant as compensation for the job those officers and servants are performing for the community. Nor is it apparently for meeting the needs of the community. Whatever the case, for Israelites who had never had a king, it may have been conveniently forgotten that kings could take a share of their harvest whether they liked it or not (Genesis 47:23–26). This would be in addition to the tithes required within the context of the religious rules and commands of the law of Moses.